This is a tutorial that documents GiNaC @value{VERSION}, an open
framework for symbolic computation within the C++ programming language.
-Copyright (C) 1999-2001 Johannes Gutenberg University Mainz, Germany
+Copyright (C) 1999-2004 Johannes Gutenberg University Mainz, Germany
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@subtitle An open framework for symbolic computation within the C++ programming language
@subtitle @value{UPDATED}
@author The GiNaC Group:
-@author Christian Bauer, Alexander Frink, Richard Kreckel
+@author Christian Bauer, Alexander Frink, Richard Kreckel, Jens Vollinga
@page
@vskip 0pt plus 1filll
-Copyright @copyright{} 1999-2001 Johannes Gutenberg University Mainz, Germany
+Copyright @copyright{} 1999-2004 Johannes Gutenberg University Mainz, Germany
@sp 2
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
present day computer algebra systems (CAS) are linguistically and
semantically impoverished. Although they are quite powerful tools for
learning math and solving particular problems they lack modern
-linguistical structures that allow for the creation of large-scale
+linguistic structures that allow for the creation of large-scale
projects. GiNaC is an attempt to overcome this situation by extending a
well established and standardized computer language (C++) by some
fundamental symbolic capabilities, thus allowing for integrated systems
@section License
The GiNaC framework for symbolic computation within the C++ programming
-language is Copyright @copyright{} 1999-2001 Johannes Gutenberg
+language is Copyright @copyright{} 1999-2004 Johannes Gutenberg
University Mainz, Germany.
This program is free software; you can redistribute it and/or
pointless) bivariate polynomial with some large coefficients:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
generates Hermite polynomials in a specified free variable.
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
Linear equation systems can be solved along with basic linear
algebra manipulations over symbolic expressions. In C++ GiNaC offers
a matrix class for this purpose but we can see what it can do using
-@command{ginsh}'s notation of double brackets to type them in:
+@command{ginsh}'s bracket notation to type them in:
@example
> lsolve(a+x*y==z,x);
y^(-1)*(z-a);
-> lsolve([3*x+5*y == 7, -2*x+10*y == -5], [x, y]);
-[x==19/8,y==-1/40]
-> M = [[ [[1, 3]], [[-3, 2]] ]];
-[[ [[1,3]], [[-3,2]] ]]
+> lsolve(@{3*x+5*y == 7, -2*x+10*y == -5@}, @{x, y@});
+@{x==19/8,y==-1/40@}
+> M = [ [1, 3], [-3, 2] ];
+[[1,3],[-3,2]]
> determinant(M);
11
> charpoly(M,lambda);
lambda^2-3*lambda+11
+> A = [ [1, 1], [2, -1] ];
+[[1,1],[2,-1]]
+> A+2*M;
+[[1,1],[2,-1]]+2*[[1,3],[-3,2]]
+> evalm(%);
+[[3,7],[-4,3]]
+> B = [ [0, 0, a], [b, 1, -b], [-1/a, 0, 0] ];
+> evalm(B^(2^12345));
+[[1,0,0],[0,1,0],[0,0,1]]
@end example
Multivariate polynomials and rational functions may be expanded,
@example
> a = x^4 + 2*x^2*y^2 + 4*x^3*y + 12*x*y^3 - 3*y^4;
--3*y^4+x^4+12*x*y^3+2*x^2*y^2+4*x^3*y
+12*x*y^3+2*x^2*y^2+4*x^3*y-3*y^4+x^4
> b = x^2 + 4*x*y - y^2;
--y^2+x^2+4*x*y
+4*x*y-y^2+x^2
> expand(a*b);
-3*y^6+x^6-24*x*y^5+43*x^2*y^4+16*x^3*y^3+17*x^4*y^2+8*x^5*y
-> collect(a*b,x);
-3*y^6+48*x*y^4+2*x^2*y^2+x^4*(-y^2+x^2+4*x*y)+4*x^3*y*(-y^2+x^2+4*x*y)
+8*x^5*y+17*x^4*y^2+43*x^2*y^4-24*x*y^5+16*x^3*y^3+3*y^6+x^6
+> collect(a+b,x);
+4*x^3*y-y^2-3*y^4+(12*y^3+4*y)*x+x^4+x^2*(1+2*y^2)
+> collect(a+b,y);
+12*x*y^3-3*y^4+(-1+2*x^2)*y^2+(4*x+4*x^3)*y+x^2+x^4
> normal(a/b);
3*y^2+x^2
@end example
> series(tgamma(x),x==0,3);
x^(-1)-Euler+(1/12*Pi^2+1/2*Euler^2)*x+
(-1/3*zeta(3)-1/12*Pi^2*Euler-1/6*Euler^3)*x^2+Order(x^3)
-> evalf(");
+> evalf(%);
x^(-1)-0.5772156649015328606+(0.9890559953279725555)*x
-(0.90747907608088628905)*x^2+Order(x^3)
> series(tgamma(2*sin(x)-2),x==Pi/2,6);
-Euler-1/12+Order((x-1/2*Pi)^3)
@end example
-Here we have made use of the @command{ginsh}-command @code{"} to pop the
+Here we have made use of the @command{ginsh}-command @code{%} to pop the
previously evaluated element from @command{ginsh}'s internal stack.
If you ever wanted to convert units in C or C++ and found this is
In order to install GiNaC on your system, some prerequisites need to be
met. First of all, you need to have a C++-compiler adhering to the
-ANSI-standard @cite{ISO/IEC 14882:1998(E)}. We used @acronym{GCC} for
-development so if you have a different compiler you are on your own.
-For the configuration to succeed you need a Posix compliant shell
-installed in @file{/bin/sh}, GNU @command{bash} is fine. Perl is needed
-by the built process as well, since some of the source files are
-automatically generated by Perl scripts. Last but not least, Bruno
-Haible's library @acronym{CLN} is extensively used and needs to be
-installed on your system. Please get it either from
-@uref{ftp://ftp.santafe.edu/pub/gnu/}, from
+ANSI-standard @cite{ISO/IEC 14882:1998(E)}. We used GCC for development
+so if you have a different compiler you are on your own. For the
+configuration to succeed you need a Posix compliant shell installed in
+@file{/bin/sh}, GNU @command{bash} is fine. Perl is needed by the built
+process as well, since some of the source files are automatically
+generated by Perl scripts. Last but not least, Bruno Haible's library
+CLN is extensively used and needs to be installed on your system.
+Please get it either from @uref{ftp://ftp.santafe.edu/pub/gnu/}, from
@uref{ftp://ftpthep.physik.uni-mainz.de/pub/gnu/, GiNaC's FTP site} or
from @uref{ftp://ftp.ilog.fr/pub/Users/haible/gnu/, Bruno Haible's FTP
site} (it is covered by GPL) and install it prior to trying to install
@end itemize
-In addition, you may specify some environment variables.
-@env{CXX} holds the path and the name of the C++ compiler
-in case you want to override the default in your path. (The
-@command{configure} script searches your path for @command{c++},
-@command{g++}, @command{gcc}, @command{CC}, @command{cxx}
-and @command{cc++} in that order.) It may be very useful to
-define some compiler flags with the @env{CXXFLAGS} environment
-variable, like optimization, debugging information and warning
-levels. If omitted, it defaults to @option{-g -O2}.
+In addition, you may specify some environment variables. @env{CXX}
+holds the path and the name of the C++ compiler in case you want to
+override the default in your path. (The @command{configure} script
+searches your path for @command{c++}, @command{g++}, @command{gcc},
+@command{CC}, @command{cxx} and @command{cc++} in that order.) It may
+be very useful to define some compiler flags with the @env{CXXFLAGS}
+environment variable, like optimization, debugging information and
+warning levels. If omitted, it defaults to @option{-g
+-O2}.@footnote{The @command{configure} script is itself generated from
+the file @file{configure.ac}. It is only distributed in packaged
+releases of GiNaC. If you got the naked sources, e.g. from CVS, you
+must generate @command{configure} along with the various
+@file{Makefile.in} by using the @command{autogen.sh} script. This will
+require a fair amount of support from your local toolchain, though.}
The whole process is illustrated in the following two
examples. (Substitute @command{setenv @var{VARIABLE} @var{value}} for
@end example
And here is a configuration for a private static GiNaC library with
-several components sitting in custom places (site-wide @acronym{GCC} and
-private @acronym{CLN}). The compiler is pursuaded to be picky and full
-assertions and debugging information are switched on:
+several components sitting in custom places (site-wide GCC and private
+CLN). The compiler is persuaded to be picky and full assertions and
+debugging information are switched on:
@example
$ export CXX=/usr/local/gnu/bin/c++
$ export CPPFLAGS="$(CPPFLAGS) -I$(HOME)/include"
-$ export CXXFLAGS="$(CXXFLAGS) -DDO_GINAC_ASSERT -ggdb -Wall -ansi -pedantic"
+$ export CXXFLAGS="$(CXXFLAGS) -DDO_GINAC_ASSERT -ggdb -Wall -pedantic"
$ export LDFLAGS="$(LDFLAGS) -L$(HOME)/lib"
$ ./configure --disable-shared --prefix=$(HOME)
@end example
to fiddle around with optimization.
Generally, the top-level Makefile runs recursively to the
-subdirectories. It is therfore safe to go into any subdirectory
-(@code{doc/}, @code{ginsh/}, ...) and simply type @code{make}
+subdirectories. It is therefore safe to go into any subdirectory
+(@code{doc/}, @code{ginsh/}, @dots{}) and simply type @code{make}
@var{target} there in case something went wrong.
@menu
* Expressions:: The fundamental GiNaC class.
+* Automatic evaluation:: Evaluation and canonicalization.
+* Error handling:: How the library reports errors.
* The Class Hierarchy:: Overview of GiNaC's classes.
* Symbols:: Symbolic objects.
* Numbers:: Numerical objects.
* Constants:: Pre-defined constants.
-* Fundamental containers:: The power, add and mul classes.
+* Fundamental containers:: Sums, products and powers.
* Lists:: Lists of expressions.
* Mathematical functions:: Mathematical functions.
* Relations:: Equality, Inequality and all that.
+* Matrices:: Matrices.
* Indexed objects:: Handling indexed quantities.
+* Non-commutative objects:: Algebras with non-commutative products.
+* Hash Maps:: A faster alternative to std::map<>.
@end menu
-@node Expressions, The Class Hierarchy, Basic Concepts, Basic Concepts
+@node Expressions, Automatic evaluation, Basic Concepts, Basic Concepts
@c node-name, next, previous, up
@section Expressions
@cindex expression (class @code{ex})
The most common class of objects a user deals with is the expression
@code{ex}, representing a mathematical object like a variable, number,
-function, sum, product, etc... Expressions may be put together to form
+function, sum, product, etc@dots{} Expressions may be put together to form
new expressions, passed as arguments to functions, and so on. Here is a
little collection of valid expressions:
hierarchy and describe the classes of objects that are handled by
@code{ex}.
+@subsection Note: Expressions and STL containers
+
+GiNaC expressions (@code{ex} objects) have value semantics (they can be
+assigned, reassigned and copied like integral types) but the operator
+@code{<} doesn't provide a well-defined ordering on them. In STL-speak,
+expressions are @samp{Assignable} but not @samp{LessThanComparable}.
+
+This implies that in order to use expressions in sorted containers such as
+@code{std::map<>} and @code{std::set<>} you have to supply a suitable
+comparison predicate. GiNaC provides such a predicate, called
+@code{ex_is_less}. For example, a set of expressions should be defined
+as @code{std::set<ex, ex_is_less>}.
+
+Unsorted containers such as @code{std::vector<>} and @code{std::list<>}
+don't pose a problem. A @code{std::vector<ex>} works as expected.
+
+@xref{Information About Expressions}, for more about comparing and ordering
+expressions.
+
+
+@node Automatic evaluation, Error handling, Expressions, Basic Concepts
+@c node-name, next, previous, up
+@section Automatic evaluation and canonicalization of expressions
+@cindex evaluation
+
+GiNaC performs some automatic transformations on expressions, to simplify
+them and put them into a canonical form. Some examples:
+
+@example
+ex MyEx1 = 2*x - 1 + x; // 3*x-1
+ex MyEx2 = x - x; // 0
+ex MyEx3 = cos(2*Pi); // 1
+ex MyEx4 = x*y/x; // y
+@end example
+
+This behavior is usually referred to as @dfn{automatic} or @dfn{anonymous
+evaluation}. GiNaC only performs transformations that are
+
+@itemize @bullet
+@item
+at most of complexity
+@tex
+$O(n\log n)$
+@end tex
+@ifnottex
+@math{O(n log n)}
+@end ifnottex
+@item
+algebraically correct, possibly except for a set of measure zero (e.g.
+@math{x/x} is transformed to @math{1} although this is incorrect for @math{x=0})
+@end itemize
+
+There are two types of automatic transformations in GiNaC that may not
+behave in an entirely obvious way at first glance:
+
+@itemize
+@item
+The terms of sums and products (and some other things like the arguments of
+symmetric functions, the indices of symmetric tensors etc.) are re-ordered
+into a canonical form that is deterministic, but not lexicographical or in
+any other way easy to guess (it almost always depends on the number and
+order of the symbols you define). However, constructing the same expression
+twice, either implicitly or explicitly, will always result in the same
+canonical form.
+@item
+Expressions of the form 'number times sum' are automatically expanded (this
+has to do with GiNaC's internal representation of sums and products). For
+example
+@example
+ex MyEx5 = 2*(x + y); // 2*x+2*y
+ex MyEx6 = z*(x + y); // z*(x+y)
+@end example
+@end itemize
+
+The general rule is that when you construct expressions, GiNaC automatically
+creates them in canonical form, which might differ from the form you typed in
+your program. This may create some awkward looking output (@samp{-y+x} instead
+of @samp{x-y}) but allows for more efficient operation and usually yields
+some immediate simplifications.
+
+@cindex @code{eval()}
+Internally, the anonymous evaluator in GiNaC is implemented by the methods
+
+@example
+ex ex::eval(int level = 0) const;
+ex basic::eval(int level = 0) const;
+@end example
+
+but unless you are extending GiNaC with your own classes or functions, there
+should never be any reason to call them explicitly. All GiNaC methods that
+transform expressions, like @code{subs()} or @code{normal()}, automatically
+re-evaluate their results.
+
+
+@node Error handling, The Class Hierarchy, Automatic evaluation, Basic Concepts
+@c node-name, next, previous, up
+@section Error handling
+@cindex exceptions
+@cindex @code{pole_error} (class)
+
+GiNaC reports run-time errors by throwing C++ exceptions. All exceptions
+generated by GiNaC are subclassed from the standard @code{exception} class
+defined in the @file{<stdexcept>} header. In addition to the predefined
+@code{logic_error}, @code{domain_error}, @code{out_of_range},
+@code{invalid_argument}, @code{runtime_error}, @code{range_error} and
+@code{overflow_error} types, GiNaC also defines a @code{pole_error}
+exception that gets thrown when trying to evaluate a mathematical function
+at a singularity.
+
+The @code{pole_error} class has a member function
+
+@example
+int pole_error::degree() const;
+@end example
+
+that returns the order of the singularity (or 0 when the pole is
+logarithmic or the order is undefined).
+
+When using GiNaC it is useful to arrange for exceptions to be caught in
+the main program even if you don't want to do any special error handling.
+Otherwise whenever an error occurs in GiNaC, it will be delegated to the
+default exception handler of your C++ compiler's run-time system which
+usually only aborts the program without giving any information what went
+wrong.
+
+Here is an example for a @code{main()} function that catches and prints
+exceptions generated by GiNaC:
+
+@example
+#include <iostream>
+#include <stdexcept>
+#include <ginac/ginac.h>
+using namespace std;
+using namespace GiNaC;
+
+int main()
+@{
+ try @{
+ ...
+ // code using GiNaC
+ ...
+ @} catch (exception &p) @{
+ cerr << p.what() << endl;
+ return 1;
+ @}
+ return 0;
+@}
+@end example
+
-@node The Class Hierarchy, Symbols, Expressions, Basic Concepts
+@node The Class Hierarchy, Symbols, Error handling, Basic Concepts
@c node-name, next, previous, up
@section The Class Hierarchy
@cindex container
@cindex atom
-To get an idea about what kinds of symbolic composits may be built we
+To get an idea about what kinds of symbolic composites may be built we
have a look at the most important classes in the class hierarchy and
some of the relations among the classes:
@item @code{numeric} @tab All kinds of numbers, @math{42}, @math{7/3*I}, @math{3.14159}@dots{}
@item @code{add} @tab Sums like @math{x+y} or @math{a-(2*b)+3}
@item @code{mul} @tab Products like @math{x*y} or @math{2*a^2*(x+y+z)/b}
+@item @code{ncmul} @tab Products of non-commutative objects
@item @code{power} @tab Exponentials such as @math{x^2}, @math{a^b},
@tex
$\sqrt{2}$
@end ifnottex
@dots{}
@item @code{pseries} @tab Power Series, e.g. @math{x-1/6*x^3+1/120*x^5+O(x^7)}
-@item @code{function} @tab A symbolic function like @math{sin(2*x)}
-@item @code{lst} @tab Lists of expressions [@math{x}, @math{2*y}, @math{3+z}]
-@item @code{matrix} @tab @math{n}x@math{m} matrices of expressions
+@item @code{function} @tab A symbolic function like
+@tex
+$\sin 2x$
+@end tex
+@ifnottex
+@math{sin(2*x)}
+@end ifnottex
+@item @code{lst} @tab Lists of expressions @{@math{x}, @math{2*y}, @math{3+z}@}
+@item @code{matrix} @tab @math{m}x@math{n} matrices of expressions
@item @code{relational} @tab A relation like the identity @math{x}@code{==}@math{y}
@item @code{indexed} @tab Indexed object like @math{A_ij}
@item @code{tensor} @tab Special tensor like the delta and metric tensors
@item @code{idx} @tab Index of an indexed object
@item @code{varidx} @tab Index with variance
+@item @code{spinidx} @tab Index with variance and dot (used in Weyl-van-der-Waerden spinor formalism)
+@item @code{wildcard} @tab Wildcard for pattern matching
+@item @code{structure} @tab Template for user-defined classes
@end multitable
@end cartouche
+
@node Symbols, Numbers, The Class Hierarchy, Basic Concepts
@c node-name, next, previous, up
@section Symbols
@cindex hierarchy of classes
@cindex atom
-Symbols are for symbolic manipulation what atoms are for chemistry. You
-can declare objects of class @code{symbol} as any other object simply by
-saying @code{symbol x,y;}. There is, however, a catch in here having to
-do with the fact that C++ is a compiled language. The information about
-the symbol's name is thrown away by the compiler but at a later stage
-you may want to print expressions holding your symbols. In order to
-avoid confusion GiNaC's symbols are able to know their own name. This
-is accomplished by declaring its name for output at construction time in
-the fashion @code{symbol x("x");}. If you declare a symbol using the
-default constructor (i.e. without string argument) the system will deal
-out a unique name. That name may not be suitable for printing but for
-internal routines when no output is desired it is often enough. We'll
-come across examples of such symbols later in this tutorial.
-
-This implies that the strings passed to symbols at construction time may
-not be used for comparing two of them. It is perfectly legitimate to
-write @code{symbol x("x"),y("x");} but it is likely to lead into
-trouble. Here, @code{x} and @code{y} are different symbols and
-statements like @code{x-y} will not be simplified to zero although the
-output @code{x-x} looks funny. Such output may also occur when there
-are two different symbols in two scopes, for instance when you call a
-function that declares a symbol with a name already existent in a symbol
-in the calling function. Again, comparing them (using @code{operator==}
-for instance) will always reveal their difference. Watch out, please.
+Symbolic indeterminates, or @dfn{symbols} for short, are for symbolic
+manipulation what atoms are for chemistry.
+
+A typical symbol definition looks like this:
+@example
+symbol x("x");
+@end example
+
+This definition actually contains three very different things:
+@itemize
+@item a C++ variable named @code{x}
+@item a @code{symbol} object stored in this C++ variable; this object
+ represents the symbol in a GiNaC expression
+@item the string @code{"x"} which is the name of the symbol, used (almost)
+ exclusively for printing expressions holding the symbol
+@end itemize
+
+Symbols have an explicit name, supplied as a string during construction,
+because in C++, variable names can't be used as values, and the C++ compiler
+throws them away during compilation.
+
+It is possible to omit the symbol name in the definition:
+@example
+symbol x;
+@end example
+
+In this case, GiNaC will assign the symbol an internal, unique name of the
+form @code{symbolNNN}. This won't affect the usability of the symbol but
+the output of your calculations will become more readable if you give your
+symbols sensible names (for intermediate expressions that are only used
+internally such anonymous symbols can be quite useful, however).
+
+Now, here is one important property of GiNaC that differentiates it from
+other computer algebra programs you may have used: GiNaC does @emph{not} use
+the names of symbols to tell them apart, but a (hidden) serial number that
+is unique for each newly created @code{symbol} object. In you want to use
+one and the same symbol in different places in your program, you must only
+create one @code{symbol} object and pass that around. If you create another
+symbol, even if it has the same name, GiNaC will treat it as a different
+indeterminate.
+
+Observe:
+@example
+ex f(int n)
+@{
+ symbol x("x");
+ return pow(x, n);
+@}
+
+int main()
+@{
+ symbol x("x");
+ ex e = f(6);
+
+ cout << e << endl;
+ // prints "x^6" which looks right, but...
+
+ cout << e.degree(x) << endl;
+ // ...this doesn't work. The symbol "x" here is different from the one
+ // in f() and in the expression returned by f(). Consequently, it
+ // prints "0".
+@}
+@end example
+
+One possibility to ensure that @code{f()} and @code{main()} use the same
+symbol is to pass the symbol as an argument to @code{f()}:
+@example
+ex f(int n, const ex & x)
+@{
+ return pow(x, n);
+@}
+
+int main()
+@{
+ symbol x("x");
+
+ // Now, f() uses the same symbol.
+ ex e = f(6, x);
+
+ cout << e.degree(x) << endl;
+ // prints "6", as expected
+@}
+@end example
+
+Another possibility would be to define a global symbol @code{x} that is used
+by both @code{f()} and @code{main()}. If you are using global symbols and
+multiple compilation units you must take special care, however. Suppose
+that you have a header file @file{globals.h} in your program that defines
+a @code{symbol x("x");}. In this case, every unit that includes
+@file{globals.h} would also get its own definition of @code{x} (because
+header files are just inlined into the source code by the C++ preprocessor),
+and hence you would again end up with multiple equally-named, but different,
+symbols. Instead, the @file{globals.h} header should only contain a
+@emph{declaration} like @code{extern symbol x;}, with the definition of
+@code{x} moved into a C++ source file such as @file{globals.cpp}.
+
+A different approach to ensuring that symbols used in different parts of
+your program are identical is to create them with a @emph{factory} function
+like this one:
+@example
+const symbol & get_symbol(const string & s)
+@{
+ static map<string, symbol> directory;
+ map<string, symbol>::iterator i = directory.find(s);
+ if (i != directory.end())
+ return i->second;
+ else
+ return directory.insert(make_pair(s, symbol(s))).first->second;
+@}
+@end example
+
+This function returns one newly constructed symbol for each name that is
+passed in, and it returns the same symbol when called multiple times with
+the same name. Using this symbol factory, we can rewrite our example like
+this:
+@example
+ex f(int n)
+@{
+ return pow(get_symbol("x"), n);
+@}
+
+int main()
+@{
+ ex e = f(6);
+
+ // Both calls of get_symbol("x") yield the same symbol.
+ cout << e.degree(get_symbol("x")) << endl;
+ // prints "6"
+@}
+@end example
+
+Instead of creating symbols from strings we could also have
+@code{get_symbol()} take, for example, an integer number as its argument.
+In this case, we would probably want to give the generated symbols names
+that include this number, which can be accomplished with the help of an
+@code{ostringstream}.
+
+In general, if you're getting weird results from GiNaC such as an expression
+@samp{x-x} that is not simplified to zero, you should check your symbol
+definitions.
+
+As we said, the names of symbols primarily serve for purposes of expression
+output. But there are actually two instances where GiNaC uses the names for
+identifying symbols: When constructing an expression from a string, and when
+recreating an expression from an archive (@pxref{Input/Output}).
+
+In addition to its name, a symbol may contain a special string that is used
+in LaTeX output:
+@example
+symbol x("x", "\\Box");
+@end example
+
+This creates a symbol that is printed as "@code{x}" in normal output, but
+as "@code{\Box}" in LaTeX code (@xref{Input/Output}, for more
+information about the different output formats of expressions in GiNaC).
+GiNaC automatically creates proper LaTeX code for symbols having names of
+greek letters (@samp{alpha}, @samp{mu}, etc.).
@cindex @code{subs()}
-Although symbols can be assigned expressions for internal reasons, you
-should not do it (and we are not going to tell you how it is done). If
-you want to replace a symbol with something else in an expression, you
-can use the expression's @code{.subs()} method (@xref{Substituting Symbols},
-for more information).
+Symbols in GiNaC can't be assigned values. If you need to store results of
+calculations and give them a name, use C++ variables of type @code{ex}.
+If you want to replace a symbol in an expression with something else, you
+can invoke the expression's @code{.subs()} method
+(@pxref{Substituting Expressions}).
+
+@cindex @code{realsymbol()}
+By default, symbols are expected to stand in for complex values, i.e. they live
+in the complex domain. As a consequence, operations like complex conjugation,
+for example (@pxref{Complex Conjugation}), do @emph{not} evaluate if applied
+to such symbols. Likewise @code{log(exp(x))} does not evaluate to @code{x},
+because of the unknown imaginary part of @code{x}.
+On the other hand, if you are sure that your symbols will hold only real values, you
+would like to have such functions evaluated. Therefore GiNaC allows you to specify
+the domain of the symbol. Instead of @code{symbol x("x");} you can write
+@code{realsymbol x("x");} to tell GiNaC that @code{x} stands in for real values.
@node Numbers, Constants, Symbols, Basic Concepts
@cindex CLN
@cindex rational
@cindex fraction
-For storing numerical things, GiNaC uses Bruno Haible's library
-@acronym{CLN}. The classes therein serve as foundation classes for
-GiNaC. @acronym{CLN} stands for Class Library for Numbers or
-alternatively for Common Lisp Numbers. In order to find out more about
-@acronym{CLN}'s internals the reader is refered to the documentation of
-that library. @inforef{Introduction, , cln}, for more
-information. Suffice to say that it is by itself build on top of another
-library, the GNU Multiple Precision library @acronym{GMP}, which is an
+For storing numerical things, GiNaC uses Bruno Haible's library CLN.
+The classes therein serve as foundation classes for GiNaC. CLN stands
+for Class Library for Numbers or alternatively for Common Lisp Numbers.
+In order to find out more about CLN's internals, the reader is referred to
+the documentation of that library. @inforef{Introduction, , cln}, for
+more information. Suffice to say that it is by itself build on top of
+another library, the GNU Multiple Precision library GMP, which is an
extremely fast library for arbitrary long integers and rationals as well
as arbitrary precision floating point numbers. It is very commonly used
-by several popular cryptographic applications. @acronym{CLN} extends
-@acronym{GMP} by several useful things: First, it introduces the complex
-number field over either reals (i.e. floating point numbers with
-arbitrary precision) or rationals. Second, it automatically converts
-rationals to integers if the denominator is unity and complex numbers to
-real numbers if the imaginary part vanishes and also correctly treats
-algebraic functions. Third it provides good implementations of
-state-of-the-art algorithms for all trigonometric and hyperbolic
-functions as well as for calculation of some useful constants.
+by several popular cryptographic applications. CLN extends GMP by
+several useful things: First, it introduces the complex number field
+over either reals (i.e. floating point numbers with arbitrary precision)
+or rationals. Second, it automatically converts rationals to integers
+if the denominator is unity and complex numbers to real numbers if the
+imaginary part vanishes and also correctly treats algebraic functions.
+Third it provides good implementations of state-of-the-art algorithms
+for all trigonometric and hyperbolic functions as well as for
+calculation of some useful constants.
The user can construct an object of class @code{numeric} in several
ways. The following example shows the four most important constructors.
integers, construction from C-float and construction from a string:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace GiNaC;
int main()
@{
- numeric two(2); // exact integer 2
+ numeric two = 2; // exact integer 2
numeric r(2,3); // exact fraction 2/3
numeric e(2.71828); // floating point number
- numeric p("3.1415926535897932385"); // floating point number
+ numeric p = "3.14159265358979323846"; // constructor from string
// Trott's constant in scientific notation:
numeric trott("1.0841015122311136151E-2");
std::cout << two*p << std::endl; // floating point 6.283...
-@}
+ ...
@end example
-Note that all those constructors are @emph{explicit} which means you are
-not allowed to write @code{numeric two=2;}. This is because the basic
-objects to be handled by GiNaC are the expressions @code{ex} and we want
-to keep things simple and wish objects like @code{pow(x,2)} to be
-handled the same way as @code{pow(x,a)}, which means that we need to
-allow a general @code{ex} as base and exponent. Therefore there is an
-implicit constructor from C-integers directly to expressions handling
-numerics at work in most of our examples. This design really becomes
-convenient when one declares own functions having more than one
-parameter but it forbids using implicit constructors because that would
-lead to compile-time ambiguities.
+@cindex @code{I}
+@cindex complex numbers
+The imaginary unit in GiNaC is a predefined @code{numeric} object with the
+name @code{I}:
-It may be tempting to construct numbers writing @code{numeric r(3/2)}.
+@example
+ ...
+ numeric z1 = 2-3*I; // exact complex number 2-3i
+ numeric z2 = 5.9+1.6*I; // complex floating point number
+@}
+@end example
+
+It may be tempting to construct fractions by writing @code{numeric r(3/2)}.
This would, however, call C's built-in operator @code{/} for integers
first and result in a numeric holding a plain integer 1. @strong{Never
use the operator @code{/} on integers} unless you know exactly what you
digits:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
@example
in 17 digits:
-0.333333333333333333
-3.14159265358979324
+0.33333333333333333334
+3.1415926535897932385
in 60 digits:
-0.333333333333333333333333333333333333333333333333333333333333333333
-3.14159265358979323846264338327950288419716939937510582097494459231
+0.33333333333333333333333333333333333333333333333333333333333333333334
+3.1415926535897932384626433832795028841971693993751058209749445923078
@end example
+@cindex rounding
+Note that the last number is not necessarily rounded as you would
+naively expect it to be rounded in the decimal system. But note also,
+that in both cases you got a couple of extra digits. This is because
+numbers are internally stored by CLN as chunks of binary digits in order
+to match your machine's word size and to not waste precision. Thus, on
+architectures with different word size, the above output might even
+differ with regard to actually computed digits.
+
It should be clear that objects of class @code{numeric} should be used
for constructing numbers or for doing arithmetic with them. The objects
one deals with most of the time are the polymorphic expressions @code{ex}.
some multiple of its denominator and test what comes out:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
holds a rational number represented as integer numerator and integer
denominator. When multiplied by 10, the denominator becomes unity and
the result is automatically converted to a pure integer again.
-Internally, the underlying @acronym{CLN} is responsible for this
-behaviour and we refer the reader to @acronym{CLN}'s documentation.
-Suffice to say that the same behaviour applies to complex numbers as
-well as return values of certain functions. Complex numbers are
-automatically converted to real numbers if the imaginary part becomes
-zero. The full set of tests that can be applied is listed in the
-following table.
+Internally, the underlying CLN is responsible for this behavior and we
+refer the reader to CLN's documentation. Suffice to say that
+the same behavior applies to complex numbers as well as return values of
+certain functions. Complex numbers are automatically converted to real
+numbers if the imaginary part becomes zero. The full set of tests that
+can be applied is listed in the following table.
@cartouche
@multitable @columnfractions .30 .70
@end multitable
@end cartouche
+@subsection Numeric functions
+
+The following functions can be applied to @code{numeric} objects and will be
+evaluated immediately:
+
+@cartouche
+@multitable @columnfractions .30 .70
+@item @strong{Name} @tab @strong{Function}
+@item @code{inverse(z)}
+@tab returns @math{1/z}
+@cindex @code{inverse()} (numeric)
+@item @code{pow(a, b)}
+@tab exponentiation @math{a^b}
+@item @code{abs(z)}
+@tab absolute value
+@item @code{real(z)}
+@tab real part
+@cindex @code{real()}
+@item @code{imag(z)}
+@tab imaginary part
+@cindex @code{imag()}
+@item @code{csgn(z)}
+@tab complex sign (returns an @code{int})
+@item @code{numer(z)}
+@tab numerator of rational or complex rational number
+@item @code{denom(z)}
+@tab denominator of rational or complex rational number
+@item @code{sqrt(z)}
+@tab square root
+@item @code{isqrt(n)}
+@tab integer square root
+@cindex @code{isqrt()}
+@item @code{sin(z)}
+@tab sine
+@item @code{cos(z)}
+@tab cosine
+@item @code{tan(z)}
+@tab tangent
+@item @code{asin(z)}
+@tab inverse sine
+@item @code{acos(z)}
+@tab inverse cosine
+@item @code{atan(z)}
+@tab inverse tangent
+@item @code{atan(y, x)}
+@tab inverse tangent with two arguments
+@item @code{sinh(z)}
+@tab hyperbolic sine
+@item @code{cosh(z)}
+@tab hyperbolic cosine
+@item @code{tanh(z)}
+@tab hyperbolic tangent
+@item @code{asinh(z)}
+@tab inverse hyperbolic sine
+@item @code{acosh(z)}
+@tab inverse hyperbolic cosine
+@item @code{atanh(z)}
+@tab inverse hyperbolic tangent
+@item @code{exp(z)}
+@tab exponential function
+@item @code{log(z)}
+@tab natural logarithm
+@item @code{Li2(z)}
+@tab dilogarithm
+@item @code{zeta(z)}
+@tab Riemann's zeta function
+@item @code{tgamma(z)}
+@tab gamma function
+@item @code{lgamma(z)}
+@tab logarithm of gamma function
+@item @code{psi(z)}
+@tab psi (digamma) function
+@item @code{psi(n, z)}
+@tab derivatives of psi function (polygamma functions)
+@item @code{factorial(n)}
+@tab factorial function @math{n!}
+@item @code{doublefactorial(n)}
+@tab double factorial function @math{n!!}
+@cindex @code{doublefactorial()}
+@item @code{binomial(n, k)}
+@tab binomial coefficients
+@item @code{bernoulli(n)}
+@tab Bernoulli numbers
+@cindex @code{bernoulli()}
+@item @code{fibonacci(n)}
+@tab Fibonacci numbers
+@cindex @code{fibonacci()}
+@item @code{mod(a, b)}
+@tab modulus in positive representation (in the range @code{[0, abs(b)-1]} with the sign of b, or zero)
+@cindex @code{mod()}
+@item @code{smod(a, b)}
+@tab modulus in symmetric representation (in the range @code{[-iquo(abs(b)-1, 2), iquo(abs(b), 2)]})
+@cindex @code{smod()}
+@item @code{irem(a, b)}
+@tab integer remainder (has the sign of @math{a}, or is zero)
+@cindex @code{irem()}
+@item @code{irem(a, b, q)}
+@tab integer remainder and quotient, @code{irem(a, b, q) == a-q*b}
+@item @code{iquo(a, b)}
+@tab integer quotient
+@cindex @code{iquo()}
+@item @code{iquo(a, b, r)}
+@tab integer quotient and remainder, @code{r == a-iquo(a, b)*b}
+@item @code{gcd(a, b)}
+@tab greatest common divisor
+@item @code{lcm(a, b)}
+@tab least common multiple
+@end multitable
+@end cartouche
+
+Most of these functions are also available as symbolic functions that can be
+used in expressions (@pxref{Mathematical functions}) or, like @code{gcd()},
+as polynomial algorithms.
+
+@subsection Converting numbers
+
+Sometimes it is desirable to convert a @code{numeric} object back to a
+built-in arithmetic type (@code{int}, @code{double}, etc.). The @code{numeric}
+class provides a couple of methods for this purpose:
+
+@cindex @code{to_int()}
+@cindex @code{to_long()}
+@cindex @code{to_double()}
+@cindex @code{to_cl_N()}
+@example
+int numeric::to_int() const;
+long numeric::to_long() const;
+double numeric::to_double() const;
+cln::cl_N numeric::to_cl_N() const;
+@end example
+
+@code{to_int()} and @code{to_long()} only work when the number they are
+applied on is an exact integer. Otherwise the program will halt with a
+message like @samp{Not a 32-bit integer}. @code{to_double()} applied on a
+rational number will return a floating-point approximation. Both
+@code{to_int()/to_long()} and @code{to_double()} discard the imaginary
+part of complex numbers.
+
@node Constants, Fundamental containers, Numbers, Basic Concepts
@c node-name, next, previous, up
@node Fundamental containers, Lists, Constants, Basic Concepts
@c node-name, next, previous, up
-@section Fundamental containers: the @code{power}, @code{add} and @code{mul} classes
+@section Sums, products and powers
@cindex polynomial
@cindex @code{add}
@cindex @code{mul}
@cindex @code{power}
-Simple polynomial expressions are written down in GiNaC pretty much like
+Simple rational expressions are written down in GiNaC pretty much like
in other CAS or like expressions involving numerical variables in C.
The necessary operators @code{+}, @code{-}, @code{*} and @code{/} have
been overloaded to achieve this goal. When you run the following
Also, expressions involving integer exponents are very frequently used,
which makes it even more dangerous to overload @code{^} since it is then
hard to distinguish between the semantics as exponentiation and the one
-for exclusive or. (It would be embarassing to return @code{1} where one
+for exclusive or. (It would be embarrassing to return @code{1} where one
has requested @code{2^3}.)
@end itemize
and safe simplifications are carried out like transforming
@code{3*x+4-x} to @code{2*x+4}.
-The general rule is that when you construct such objects, GiNaC
-automatically creates them in canonical form, which might differ from
-the form you typed in your program. This allows for rapid comparison of
-expressions, since after all @code{a-a} is simply zero. Note, that the
-canonical form is not necessarily lexicographical ordering or in any way
-easily guessable. It is only guaranteed that constructing the same
-expression twice, either implicitly or explicitly, results in the same
-canonical form.
-
@node Lists, Mathematical functions, Fundamental containers, Basic Concepts
@c node-name, next, previous, up
@cindex @code{op()}
@cindex @code{append()}
@cindex @code{prepend()}
+@cindex @code{remove_first()}
+@cindex @code{remove_last()}
+@cindex @code{remove_all()}
-The GiNaC class @code{lst} serves for holding a list of arbitrary expressions.
-These are sometimes used to supply a variable number of arguments of the same
-type to GiNaC methods such as @code{subs()} and @code{to_rational()}, so you
-should have a basic understanding about them.
+The GiNaC class @code{lst} serves for holding a @dfn{list} of arbitrary
+expressions. They are not as ubiquitous as in many other computer algebra
+packages, but are sometimes used to supply a variable number of arguments of
+the same type to GiNaC methods such as @code{subs()} and some @code{matrix}
+constructors, so you should have a basic understanding of them.
-Lists of up to 15 expressions can be directly constructed from single
+Lists can be constructed by assigning a comma-separated sequence of
expressions:
@example
@{
symbol x("x"), y("y");
- lst l(x, 2, y, x+y);
- // now, l is a list holding the expressions 'x', '2', 'y', and 'x+y'
- // ...
+ lst l;
+ l = x, 2, y, x+y;
+ // now, l is a list holding the expressions 'x', '2', 'y', and 'x+y',
+ // in that order
+ ...
+@end example
+
+There are also constructors that allow direct creation of lists of up to
+16 expressions, which is often more convenient but slightly less efficient:
+
+@example
+ ...
+ // This produces the same list 'l' as above:
+ // lst l(x, 2, y, x+y);
+ // lst l = lst(x, 2, y, x+y);
+ ...
@end example
Use the @code{nops()} method to determine the size (number of expressions) of
-a list and the @code{op()} method to access individual elements:
+a list and the @code{op()} method or the @code{[]} operator to access
+individual elements:
@example
- // ...
- cout << l.nops() << endl; // prints '4'
- cout << l.op(2) << " " << l.op(0) << endl; // prints 'y x'
- // ...
+ ...
+ cout << l.nops() << endl; // prints '4'
+ cout << l.op(2) << " " << l[0] << endl; // prints 'y x'
+ ...
@end example
-Finally you can append or prepend an expression to a list with the
-@code{append()} and @code{prepend()} methods:
+As with the standard @code{list<T>} container, accessing random elements of a
+@code{lst} is generally an operation of order @math{O(N)}. Faster read-only
+sequential access to the elements of a list is possible with the
+iterator types provided by the @code{lst} class:
@example
- // ...
- l.append(4*x); // l is now [x, 2, y, x+y, 4*x]
- l.prepend(0); // l is now [0, x, 2, y, x+y, 4*x]
+typedef ... lst::const_iterator;
+typedef ... lst::const_reverse_iterator;
+lst::const_iterator lst::begin() const;
+lst::const_iterator lst::end() const;
+lst::const_reverse_iterator lst::rbegin() const;
+lst::const_reverse_iterator lst::rend() const;
+@end example
+
+For example, to print the elements of a list individually you can use:
+
+@example
+ ...
+ // O(N)
+ for (lst::const_iterator i = l.begin(); i != l.end(); ++i)
+ cout << *i << endl;
+ ...
+@end example
+
+which is one order faster than
+
+@example
+ ...
+ // O(N^2)
+ for (size_t i = 0; i < l.nops(); ++i)
+ cout << l.op(i) << endl;
+ ...
+@end example
+
+These iterators also allow you to use some of the algorithms provided by
+the C++ standard library:
+
+@example
+ ...
+ // print the elements of the list (requires #include <iterator>)
+ std::copy(l.begin(), l.end(), ostream_iterator<ex>(cout, "\n"));
+
+ // sum up the elements of the list (requires #include <numeric>)
+ ex sum = std::accumulate(l.begin(), l.end(), ex(0));
+ cout << sum << endl; // prints '2+2*x+2*y'
+ ...
+@end example
+
+@code{lst} is one of the few GiNaC classes that allow in-place modifications
+(the only other one is @code{matrix}). You can modify single elements:
+
+@example
+ ...
+ l[1] = 42; // l is now @{x, 42, y, x+y@}
+ l.let_op(1) = 7; // l is now @{x, 7, y, x+y@}
+ ...
+@end example
+
+You can append or prepend an expression to a list with the @code{append()}
+and @code{prepend()} methods:
+
+@example
+ ...
+ l.append(4*x); // l is now @{x, 7, y, x+y, 4*x@}
+ l.prepend(0); // l is now @{0, x, 7, y, x+y, 4*x@}
+ ...
+@end example
+
+You can remove the first or last element of a list with @code{remove_first()}
+and @code{remove_last()}:
+
+@example
+ ...
+ l.remove_first(); // l is now @{x, 7, y, x+y, 4*x@}
+ l.remove_last(); // l is now @{x, 7, y, x+y@}
+ ...
+@end example
+
+You can remove all the elements of a list with @code{remove_all()}:
+
+@example
+ ...
+ l.remove_all(); // l is now empty
+ ...
+@end example
+
+You can bring the elements of a list into a canonical order with @code{sort()}:
+
+@example
+ ...
+ lst l1, l2;
+ l1 = x, 2, y, x+y;
+ l2 = 2, x+y, x, y;
+ l1.sort();
+ l2.sort();
+ // l1 and l2 are now equal
+ ...
+@end example
+
+Finally, you can remove all but the first element of consecutive groups of
+elements with @code{unique()}:
+
+@example
+ ...
+ lst l3;
+ l3 = x, 2, 2, 2, y, x+y, y+x;
+ l3.unique(); // l3 is now @{x, 2, y, x+y@}
@}
@end example
instance, all trigonometric and hyperbolic functions are implemented
(@xref{Built-in Functions}, for a complete list).
-These functions are all objects of class @code{function}. They accept
-one or more expressions as arguments and return one expression. If the
-arguments are not numerical, the evaluation of the function may be
-halted, as it does in the next example, showing how a function returns
-itself twice and finally an expression that may be really useful:
+These functions (better called @emph{pseudofunctions}) are all objects
+of class @code{function}. They accept one or more expressions as
+arguments and return one expression. If the arguments are not
+numerical, the evaluation of the function may be halted, as it does in
+the next example, showing how a function returns itself twice and
+finally an expression that may be really useful:
@cindex Gamma function
@cindex @code{subs()}
expansion and so on. Read the next chapter in order to learn more about
this.
+It must be noted that these pseudofunctions are created by inline
+functions, where the argument list is templated. This means that
+whenever you call @code{GiNaC::sin(1)} it is equivalent to
+@code{sin(ex(1))} and will therefore not result in a floating point
+number. Unless of course the function prototype is explicitly
+overridden -- which is the case for arguments of type @code{numeric}
+(not wrapped inside an @code{ex}). Hence, in order to obtain a floating
+point number of class @code{numeric} you should call
+@code{sin(numeric(1))}. This is almost the same as calling
+@code{sin(1).evalf()} except that the latter will return a numeric
+wrapped inside an @code{ex}.
-@node Relations, Indexed objects, Mathematical functions, Basic Concepts
+
+@node Relations, Matrices, Mathematical functions, Basic Concepts
@c node-name, next, previous, up
@section Relations
@cindex @code{relational} (class)
@code{expand()} must be called explicitly.
-@node Indexed objects, Methods and Functions, Relations, Basic Concepts
+@node Matrices, Indexed objects, Relations, Basic Concepts
@c node-name, next, previous, up
-@section Indexed objects
+@section Matrices
+@cindex @code{matrix} (class)
-GiNaC allows you to handle expressions containing general indexed objects in
-arbitrary spaces. It is also able to canonicalize and simplify such
-expressions and perform symbolic dummy index summations. There are a number
-of predefined indexed objects provided, like delta and metric tensors.
+A @dfn{matrix} is a two-dimensional array of expressions. The elements of a
+matrix with @math{m} rows and @math{n} columns are accessed with two
+@code{unsigned} indices, the first one in the range 0@dots{}@math{m-1}, the
+second one in the range 0@dots{}@math{n-1}.
+
+There are a couple of ways to construct matrices, with or without preset
+elements. The constructor
+
+@example
+matrix::matrix(unsigned r, unsigned c);
+@end example
+
+creates a matrix with @samp{r} rows and @samp{c} columns with all elements
+set to zero.
+
+The fastest way to create a matrix with preinitialized elements is to assign
+a list of comma-separated expressions to an empty matrix (see below for an
+example). But you can also specify the elements as a (flat) list with
+
+@example
+matrix::matrix(unsigned r, unsigned c, const lst & l);
+@end example
+
+The function
+
+@cindex @code{lst_to_matrix()}
+@example
+ex lst_to_matrix(const lst & l);
+@end example
+
+constructs a matrix from a list of lists, each list representing a matrix row.
+
+There is also a set of functions for creating some special types of
+matrices:
+
+@cindex @code{diag_matrix()}
+@cindex @code{unit_matrix()}
+@cindex @code{symbolic_matrix()}
+@example
+ex diag_matrix(const lst & l);
+ex unit_matrix(unsigned x);
+ex unit_matrix(unsigned r, unsigned c);
+ex symbolic_matrix(unsigned r, unsigned c, const string & base_name);
+ex symbolic_matrix(unsigned r, unsigned c, const string & base_name, const string & tex_base_name);
+@end example
+
+@code{diag_matrix()} constructs a diagonal matrix given the list of diagonal
+elements. @code{unit_matrix()} creates an @samp{x} by @samp{x} (or @samp{r}
+by @samp{c}) unit matrix. And finally, @code{symbolic_matrix} constructs a
+matrix filled with newly generated symbols made of the specified base name
+and the position of each element in the matrix.
+
+Matrix elements can be accessed and set using the parenthesis (function call)
+operator:
+
+@example
+const ex & matrix::operator()(unsigned r, unsigned c) const;
+ex & matrix::operator()(unsigned r, unsigned c);
+@end example
+
+It is also possible to access the matrix elements in a linear fashion with
+the @code{op()} method. But C++-style subscripting with square brackets
+@samp{[]} is not available.
+
+Here are a couple of examples for constructing matrices:
+
+@example
+@{
+ symbol a("a"), b("b");
+
+ matrix M(2, 2);
+ M = a, 0,
+ 0, b;
+ cout << M << endl;
+ // -> [[a,0],[0,b]]
+
+ matrix M2(2, 2);
+ M2(0, 0) = a;
+ M2(1, 1) = b;
+ cout << M2 << endl;
+ // -> [[a,0],[0,b]]
+
+ cout << matrix(2, 2, lst(a, 0, 0, b)) << endl;
+ // -> [[a,0],[0,b]]
+
+ cout << lst_to_matrix(lst(lst(a, 0), lst(0, b))) << endl;
+ // -> [[a,0],[0,b]]
+
+ cout << diag_matrix(lst(a, b)) << endl;
+ // -> [[a,0],[0,b]]
+
+ cout << unit_matrix(3) << endl;
+ // -> [[1,0,0],[0,1,0],[0,0,1]]
+
+ cout << symbolic_matrix(2, 3, "x") << endl;
+ // -> [[x00,x01,x02],[x10,x11,x12]]
+@}
+@end example
+
+@cindex @code{transpose()}
+There are three ways to do arithmetic with matrices. The first (and most
+direct one) is to use the methods provided by the @code{matrix} class:
+
+@example
+matrix matrix::add(const matrix & other) const;
+matrix matrix::sub(const matrix & other) const;
+matrix matrix::mul(const matrix & other) const;
+matrix matrix::mul_scalar(const ex & other) const;
+matrix matrix::pow(const ex & expn) const;
+matrix matrix::transpose() const;
+@end example
+
+All of these methods return the result as a new matrix object. Here is an
+example that calculates @math{A*B-2*C} for three matrices @math{A}, @math{B}
+and @math{C}:
+
+@example
+@{
+ matrix A(2, 2), B(2, 2), C(2, 2);
+ A = 1, 2,
+ 3, 4;
+ B = -1, 0,
+ 2, 1;
+ C = 8, 4,
+ 2, 1;
+
+ matrix result = A.mul(B).sub(C.mul_scalar(2));
+ cout << result << endl;
+ // -> [[-13,-6],[1,2]]
+ ...
+@}
+@end example
+
+@cindex @code{evalm()}
+The second (and probably the most natural) way is to construct an expression
+containing matrices with the usual arithmetic operators and @code{pow()}.
+For efficiency reasons, expressions with sums, products and powers of
+matrices are not automatically evaluated in GiNaC. You have to call the
+method
+
+@example
+ex ex::evalm() const;
+@end example
+
+to obtain the result:
+
+@example
+@{
+ ...
+ ex e = A*B - 2*C;
+ cout << e << endl;
+ // -> [[1,2],[3,4]]*[[-1,0],[2,1]]-2*[[8,4],[2,1]]
+ cout << e.evalm() << endl;
+ // -> [[-13,-6],[1,2]]
+ ...
+@}
+@end example
+
+The non-commutativity of the product @code{A*B} in this example is
+automatically recognized by GiNaC. There is no need to use a special
+operator here. @xref{Non-commutative objects}, for more information about
+dealing with non-commutative expressions.
+
+Finally, you can work with indexed matrices and call @code{simplify_indexed()}
+to perform the arithmetic:
+
+@example
+@{
+ ...
+ idx i(symbol("i"), 2), j(symbol("j"), 2), k(symbol("k"), 2);
+ e = indexed(A, i, k) * indexed(B, k, j) - 2 * indexed(C, i, j);
+ cout << e << endl;
+ // -> -2*[[8,4],[2,1]].i.j+[[-1,0],[2,1]].k.j*[[1,2],[3,4]].i.k
+ cout << e.simplify_indexed() << endl;
+ // -> [[-13,-6],[1,2]].i.j
+@}
+@end example
+
+Using indices is most useful when working with rectangular matrices and
+one-dimensional vectors because you don't have to worry about having to
+transpose matrices before multiplying them. @xref{Indexed objects}, for
+more information about using matrices with indices, and about indices in
+general.
+
+The @code{matrix} class provides a couple of additional methods for
+computing determinants, traces, characteristic polynomials and ranks:
+
+@cindex @code{determinant()}
+@cindex @code{trace()}
+@cindex @code{charpoly()}
+@cindex @code{rank()}
+@example
+ex matrix::determinant(unsigned algo=determinant_algo::automatic) const;
+ex matrix::trace() const;
+ex matrix::charpoly(const ex & lambda) const;
+unsigned matrix::rank() const;
+@end example
+
+The @samp{algo} argument of @code{determinant()} allows to select
+between different algorithms for calculating the determinant. The
+asymptotic speed (as parametrized by the matrix size) can greatly differ
+between those algorithms, depending on the nature of the matrix'
+entries. The possible values are defined in the @file{flags.h} header
+file. By default, GiNaC uses a heuristic to automatically select an
+algorithm that is likely (but not guaranteed) to give the result most
+quickly.
+
+@cindex @code{inverse()} (matrix)
+@cindex @code{solve()}
+Matrices may also be inverted using the @code{ex matrix::inverse()}
+method and linear systems may be solved with:
+
+@example
+matrix matrix::solve(const matrix & vars, const matrix & rhs, unsigned algo=solve_algo::automatic) const;
+@end example
+
+Assuming the matrix object this method is applied on is an @code{m}
+times @code{n} matrix, then @code{vars} must be a @code{n} times
+@code{p} matrix of symbolic indeterminates and @code{rhs} a @code{m}
+times @code{p} matrix. The returned matrix then has dimension @code{n}
+times @code{p} and in the case of an underdetermined system will still
+contain some of the indeterminates from @code{vars}. If the system is
+overdetermined, an exception is thrown.
+
+
+@node Indexed objects, Non-commutative objects, Matrices, Basic Concepts
+@c node-name, next, previous, up
+@section Indexed objects
+
+GiNaC allows you to handle expressions containing general indexed objects in
+arbitrary spaces. It is also able to canonicalize and simplify such
+expressions and perform symbolic dummy index summations. There are a number
+of predefined indexed objects provided, like delta and metric tensors.
There are few restrictions placed on indexed objects and their indices and
it is easy to construct nonsense expressions, but our intention is to
a @dfn{value} and a @dfn{dimension} (which is the dimension of the space
the index lives in) which can both be arbitrary expressions but are usually
a number or a simple symbol. In addition, indices of class @code{varidx} have
-a @dfn{variance} (they can be co- or contravariant).
+a @dfn{variance} (they can be co- or contravariant), and indices of class
+@code{spinidx} have a variance and can be @dfn{dotted} or @dfn{undotted}.
@item Indexed objects are of class @code{indexed} or a subclass. They
contain a @dfn{base expression} (which is the expression being indexed), and
@end itemize
@strong{Note:} when printing expressions, covariant indices and indices
-without variance are denoted @samp{.i} while contravariant indices are denoted
-@samp{~i}. In the following, we are going to use that notation in the text
-so instead of @math{A^i_jk} we will write @samp{A~i.j.k}. Index dimensions
-are not visible in the output.
+without variance are denoted @samp{.i} while contravariant indices are
+denoted @samp{~i}. Dotted indices have a @samp{*} in front of the index
+value. In the following, we are going to use that notation in the text so
+instead of @math{A^i_jk} we will write @samp{A~i.j.k}. Index dimensions are
+not visible in the output.
A simple example shall illustrate the concepts:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
symbol A("A");
cout << indexed(A, i, j) << endl;
// -> A.i.j
+ cout << index_dimensions << indexed(A, i, j) << endl;
+ // -> A.i[3].j[3]
+ cout << dflt; // reset cout to default output format (dimensions hidden)
...
@end example
the symbol @code{A} as its base expression and the two indices @code{i} and
@code{j}.
+The dimensions of indices are normally not visible in the output, but one
+can request them to be printed with the @code{index_dimensions} manipulator,
+as shown above.
+
Note the difference between the indices @code{i} and @code{j} which are of
-class @code{idx}, and the index values which are the sybols @code{i_sym}
+class @code{idx}, and the index values which are the symbols @code{i_sym}
and @code{j_sym}. The indices of indexed objects cannot directly be symbols
or numbers but must be index objects. For example, the following is not
correct and will raise an exception:
The methods
@example
-ex idx::get_value(void);
-ex idx::get_dimension(void);
+ex idx::get_value();
+ex idx::get_dimension();
@end example
return the value and dimension of an @code{idx} object. If you have an index
in an expression, such as returned by calling @code{.op()} on an indexed
object, you can get a reference to the @code{idx} object with the function
-@code{ex_to_idx()} on the expression.
+@code{ex_to<idx>()} on the expression.
There are also the methods
@example
-bool idx::is_numeric(void);
-bool idx::is_symbolic(void);
-bool idx::is_dim_numeric(void);
-bool idx::is_dim_symbolic(void);
+bool idx::is_numeric();
+bool idx::is_symbolic();
+bool idx::is_dim_numeric();
+bool idx::is_dim_symbolic();
@end example
for checking whether the value and dimension are numeric or symbolic
constructor. The two methods
@example
-bool varidx::is_covariant(void);
-bool varidx::is_contravariant(void);
+bool varidx::is_covariant();
+bool varidx::is_contravariant();
@end example
-allow you to check the variance of a @code{varidx} object (use @code{ex_to_varidx()}
+allow you to check the variance of a @code{varidx} object (use @code{ex_to<varidx>()}
to get the object reference from an expression). There's also the very useful
method
@example
-ex varidx::toggle_variance(void);
+ex varidx::toggle_variance();
@end example
which makes a new index with the same value and dimension but the opposite
variance. By using it you only have to define the index once.
+@cindex @code{spinidx} (class)
+The @code{spinidx} class provides dotted and undotted variant indices, as
+used in the Weyl-van-der-Waerden spinor formalism:
+
+@example
+ ...
+ symbol K("K"), C_sym("C"), D_sym("D");
+ spinidx C(C_sym, 2), D(D_sym); // default is 2-dimensional,
+ // contravariant, undotted
+ spinidx C_co(C_sym, 2, true); // covariant index
+ spinidx D_dot(D_sym, 2, false, true); // contravariant, dotted
+ spinidx D_co_dot(D_sym, 2, true, true); // covariant, dotted
+
+ cout << indexed(K, C, D) << endl;
+ // -> K~C~D
+ cout << indexed(K, C_co, D_dot) << endl;
+ // -> K.C~*D
+ cout << indexed(K, D_co_dot, D) << endl;
+ // -> K.*D~D
+ ...
+@end example
+
+A @code{spinidx} is a @code{varidx} with an additional flag that marks it as
+dotted or undotted. The default is undotted but this can be overridden by
+supplying a fourth argument to the @code{spinidx} constructor. The two
+methods
+
+@example
+bool spinidx::is_dotted();
+bool spinidx::is_undotted();
+@end example
+
+allow you to check whether or not a @code{spinidx} object is dotted (use
+@code{ex_to<spinidx>()} to get the object reference from an expression).
+Finally, the two methods
+
+@example
+ex spinidx::toggle_dot();
+ex spinidx::toggle_variance_dot();
+@end example
+
+create a new index with the same value and dimension but opposite dottedness
+and the same or opposite variance.
+
@subsection Substituting indices
@cindex @code{subs()}
Sometimes you will want to substitute one symbolic index with another
symbolic or numeric index, for example when calculating one specific element
of a tensor expression. This is done with the @code{.subs()} method, as it
-is done for symbols (see @ref{Substituting Symbols}).
+is done for symbols (see @ref{Substituting Expressions}).
You have two possibilities here. You can either substitute the whole index
by another index or expression:
@end example
@subsection Symmetries
+@cindex @code{symmetry} (class)
+@cindex @code{sy_none()}
+@cindex @code{sy_symm()}
+@cindex @code{sy_anti()}
+@cindex @code{sy_cycl()}
+
+Indexed objects can have certain symmetry properties with respect to their
+indices. Symmetries are specified as a tree of objects of class @code{symmetry}
+that is constructed with the helper functions
-Indexed objects can be declared as being totally symmetric or antisymmetric
-with respect to their indices. In this case, GiNaC will automatically bring
-the indices into a canonical order which allows for some immediate
-simplifications:
+@example
+symmetry sy_none(...);
+symmetry sy_symm(...);
+symmetry sy_anti(...);
+symmetry sy_cycl(...);
+@end example
+
+@code{sy_none()} stands for no symmetry, @code{sy_symm()} and @code{sy_anti()}
+specify fully symmetric or antisymmetric, respectively, and @code{sy_cycl()}
+represents a cyclic symmetry. Each of these functions accepts up to four
+arguments which can be either symmetry objects themselves or unsigned integer
+numbers that represent an index position (counting from 0). A symmetry
+specification that consists of only a single @code{sy_symm()}, @code{sy_anti()}
+or @code{sy_cycl()} with no arguments specifies the respective symmetry for
+all indices.
+
+Here are some examples of symmetry definitions:
+
+@example
+ ...
+ // No symmetry:
+ e = indexed(A, i, j);
+ e = indexed(A, sy_none(), i, j); // equivalent
+ e = indexed(A, sy_none(0, 1), i, j); // equivalent
+
+ // Symmetric in all three indices:
+ e = indexed(A, sy_symm(), i, j, k);
+ e = indexed(A, sy_symm(0, 1, 2), i, j, k); // equivalent
+ e = indexed(A, sy_symm(2, 0, 1), i, j, k); // same symmetry, but yields a
+ // different canonical order
+
+ // Symmetric in the first two indices only:
+ e = indexed(A, sy_symm(0, 1), i, j, k);
+ e = indexed(A, sy_none(sy_symm(0, 1), 2), i, j, k); // equivalent
+
+ // Antisymmetric in the first and last index only (index ranges need not
+ // be contiguous):
+ e = indexed(A, sy_anti(0, 2), i, j, k);
+ e = indexed(A, sy_none(sy_anti(0, 2), 1), i, j, k); // equivalent
+
+ // An example of a mixed symmetry: antisymmetric in the first two and
+ // last two indices, symmetric when swapping the first and last index
+ // pairs (like the Riemann curvature tensor):
+ e = indexed(A, sy_symm(sy_anti(0, 1), sy_anti(2, 3)), i, j, k, l);
+
+ // Cyclic symmetry in all three indices:
+ e = indexed(A, sy_cycl(), i, j, k);
+ e = indexed(A, sy_cycl(0, 1, 2), i, j, k); // equivalent
+
+ // The following examples are invalid constructions that will throw
+ // an exception at run time.
+
+ // An index may not appear multiple times:
+ e = indexed(A, sy_symm(0, 0, 1), i, j, k); // ERROR
+ e = indexed(A, sy_none(sy_symm(0, 1), sy_anti(0, 2)), i, j, k); // ERROR
+
+ // Every child of sy_symm(), sy_anti() and sy_cycl() must refer to the
+ // same number of indices:
+ e = indexed(A, sy_symm(sy_anti(0, 1), 2), i, j, k); // ERROR
+
+ // And of course, you cannot specify indices which are not there:
+ e = indexed(A, sy_symm(0, 1, 2, 3), i, j, k); // ERROR
+ ...
+@end example
+
+If you need to specify more than four indices, you have to use the
+@code{.add()} method of the @code{symmetry} class. For example, to specify
+full symmetry in the first six indices you would write
+@code{sy_symm(0, 1, 2, 3).add(4).add(5)}.
+
+If an indexed object has a symmetry, GiNaC will automatically bring the
+indices into a canonical order which allows for some immediate simplifications:
@example
...
- cout << indexed(A, indexed::symmetric, i, j)
- + indexed(A, indexed::symmetric, j, i) << endl;
+ cout << indexed(A, sy_symm(), i, j)
+ + indexed(A, sy_symm(), j, i) << endl;
// -> 2*A.j.i
- cout << indexed(B, indexed::antisymmetric, i, j)
- + indexed(B, indexed::antisymmetric, j, j) << endl;
- // -> -B.j.i
- cout << indexed(B, indexed::antisymmetric, i, j)
- + indexed(B, indexed::antisymmetric, j, i) << endl;
+ cout << indexed(B, sy_anti(), i, j)
+ + indexed(B, sy_anti(), j, i) << endl;
+ // -> 0
+ cout << indexed(B, sy_anti(), i, j, k)
+ - indexed(B, sy_anti(), j, k, i) << endl;
// -> 0
...
@end example
@cindex @code{get_free_indices()}
-@cindex Dummy index
+@cindex dummy index
@subsection Dummy indices
GiNaC treats certain symbolic index pairs as @dfn{dummy indices} meaning
dummy nor free indices.
To be recognized as a dummy index pair, the two indices must be of the same
-class and dimension and their value must be the same single symbol (an index
-like @samp{2*n+1} is never a dummy index). If the indices are of class
-@code{varidx}, they must also be of opposite variance.
+class and their value must be the same single symbol (an index like
+@samp{2*n+1} is never a dummy index). If the indices are of class
+@code{varidx} they must also be of opposite variance; if they are of class
+@code{spinidx} they must be both dotted or both undotted.
The method @code{.get_free_indices()} returns a vector containing the free
indices of an expression. It also checks that the free indices of the terms
there is the method
@example
-ex ex::simplify_indexed(void);
+ex ex::simplify_indexed();
ex ex::simplify_indexed(const scalar_products & sp);
@end example
@itemize
@item it checks the consistency of free indices in sums in the same way
@code{get_free_indices()} does
+@item it tries to give dummy indices that appear in different terms of a sum
+ the same name to allow simplifications like @math{a_i*b_i-a_j*b_j=0}
@item it (symbolically) calculates all possible dummy index summations/contractions
with the predefined tensors (this will be explained in more detail in the
next section)
+@item it detects contractions that vanish for symmetry reasons, for example
+ the contraction of a symmetric and a totally antisymmetric tensor
@item as a special case of dummy index summation, it can replace scalar products
of two tensors with a user-defined value
@end itemize
@code{simplify_indexed()} will replace all scalar products of indexed
objects that have the symbols @code{A} and @code{B} as base expressions
with the single value 0. The number, type and dimension of the indices
-doesn't matter; @samp{A~mu~nu*B.mu.nu} would also be replaced by 0.
+don't matter; @samp{A~mu~nu*B.mu.nu} would also be replaced by 0.
@cindex @code{expand()}
The example above also illustrates a feature of the @code{expand()} method:
@subsubsection Delta tensor
The delta tensor takes two indices, is symmetric and has the matrix
-representation @code{diag(1,1,1,...)}. It is constructed by the function
+representation @code{diag(1, 1, 1, ...)}. It is constructed by the function
@code{delta_tensor()}:
@example
@}
@end example
+@cindex @code{spinor_metric()}
+@subsubsection Spinor metric tensor
+
+The function @code{spinor_metric()} creates an antisymmetric tensor with
+two indices that is used to raise/lower indices of 2-component spinors.
+It is output as @samp{eps}:
+
+@example
+@{
+ symbol psi("psi");
+
+ spinidx A(symbol("A")), B(symbol("B")), C(symbol("C"));
+ ex A_co = A.toggle_variance(), B_co = B.toggle_variance();
+
+ e = spinor_metric(A, B) * indexed(psi, B_co);
+ cout << e.simplify_indexed() << endl;
+ // -> psi~A
+
+ e = spinor_metric(A, B) * indexed(psi, A_co);
+ cout << e.simplify_indexed() << endl;
+ // -> -psi~B
+
+ e = spinor_metric(A_co, B_co) * indexed(psi, B);
+ cout << e.simplify_indexed() << endl;
+ // -> -psi.A
+
+ e = spinor_metric(A_co, B_co) * indexed(psi, A);
+ cout << e.simplify_indexed() << endl;
+ // -> psi.B
+
+ e = spinor_metric(A_co, B_co) * spinor_metric(A, B);
+ cout << e.simplify_indexed() << endl;
+ // -> 2
+
+ e = spinor_metric(A_co, B_co) * spinor_metric(B, C);
+ cout << e.simplify_indexed() << endl;
+ // -> -delta.A~C
+@}
+@end example
+
+The matrix representation of the spinor metric is @code{[[0, 1], [-1, 0]]}.
+
+@cindex @code{epsilon_tensor()}
+@cindex @code{lorentz_eps()}
@subsubsection Epsilon tensor
The epsilon tensor is totally antisymmetric, its number of indices is equal
to the dimension of the index space (the indices must all be of the same
numeric dimension), and @samp{eps.1.2.3...} (resp. @samp{eps~0~1~2...}) is
-defined to be 1. Its behaviour with indices that have a variance also
+defined to be 1. Its behavior with indices that have a variance also
depends on the signature of the metric. Epsilon tensors are output as
@samp{eps}.
dimensions, the last function creates an epsilon tensor in a 4-dimensional
Minkowski space (the last @code{bool} argument specifies whether the metric
has negative or positive signature, as in the case of the Minkowski metric
-tensor).
+tensor):
+
+@example
+@{
+ varidx mu(symbol("mu"), 4), nu(symbol("nu"), 4), rho(symbol("rho"), 4),
+ sig(symbol("sig"), 4), lam(symbol("lam"), 4), bet(symbol("bet"), 4);
+ e = lorentz_eps(mu, nu, rho, sig) *
+ lorentz_eps(mu.toggle_variance(), nu.toggle_variance(), lam, bet);
+ cout << simplify_indexed(e) << endl;
+ // -> 2*eta~bet~rho*eta~sig~lam-2*eta~sig~bet*eta~rho~lam
+
+ idx i(symbol("i"), 3), j(symbol("j"), 3), k(symbol("k"), 3);
+ symbol A("A"), B("B");
+ e = epsilon_tensor(i, j, k) * indexed(A, j) * indexed(B, k);
+ cout << simplify_indexed(e) << endl;
+ // -> -B.k*A.j*eps.i.k.j
+ e = epsilon_tensor(i, j, k) * indexed(A, j) * indexed(A, k);
+ cout << simplify_indexed(e) << endl;
+ // -> 0
+@}
+@end example
@subsection Linear algebra
idx i(symbol("i"), 2), j(symbol("j"), 2);
symbol x("x"), y("y");
- matrix A(2, 2, lst(1, 2, 3, 4)), X(2, 1, lst(x, y));
+ // A is a 2x2 matrix, X is a 2x1 vector
+ matrix A(2, 2), X(2, 1);
+ A = 1, 2,
+ 3, 4;
+ X = x, y;
cout << indexed(A, i, i) << endl;
// -> 5
ex e = indexed(A, i, j) * indexed(X, j);
cout << e.simplify_indexed() << endl;
- // -> [[ [[2*y+x]], [[4*y+3*x]] ]].i
+ // -> [[2*y+x],[4*y+3*x]].i
e = indexed(A, i, j) * indexed(X, i) + indexed(X, j) * 2;
cout << e.simplify_indexed() << endl;
- // -> [[ [[3*y+3*x,6*y+2*x]] ]].j
+ // -> [[3*y+3*x,6*y+2*x]].j
@}
@end example
You can of course obtain the same results with the @code{matrix::add()},
-@code{matrix::mul()} and @code{matrix::trace()} methods but with indices you
-don't have to worry about transposing matrices.
+@code{matrix::mul()} and @code{matrix::trace()} methods (@pxref{Matrices})
+but with indices you don't have to worry about transposing matrices.
Matrix indices always start at 0 and their dimension must match the number
of rows/columns of the matrix. Matrices with one row or one column are
of the metric tensor.
-@node Methods and Functions, Information About Expressions, Indexed objects, Top
+@node Non-commutative objects, Hash Maps, Indexed objects, Basic Concepts
@c node-name, next, previous, up
-@chapter Methods and Functions
-@cindex polynomial
+@section Non-commutative objects
-In this chapter the most important algorithms provided by GiNaC will be
-described. Some of them are implemented as functions on expressions,
-others are implemented as methods provided by expression objects. If
-they are methods, there exists a wrapper function around it, so you can
-alternatively call it in a functional way as shown in the simple
-example:
+GiNaC is equipped to handle certain non-commutative algebras. Three classes of
+non-commutative objects are built-in which are mostly of use in high energy
+physics:
+
+@itemize
+@item Clifford (Dirac) algebra (class @code{clifford})
+@item su(3) Lie algebra (class @code{color})
+@item Matrices (unindexed) (class @code{matrix})
+@end itemize
+
+The @code{clifford} and @code{color} classes are subclasses of
+@code{indexed} because the elements of these algebras usually carry
+indices. The @code{matrix} class is described in more detail in
+@ref{Matrices}.
+
+Unlike most computer algebra systems, GiNaC does not primarily provide an
+operator (often denoted @samp{&*}) for representing inert products of
+arbitrary objects. Rather, non-commutativity in GiNaC is a property of the
+classes of objects involved, and non-commutative products are formed with
+the usual @samp{*} operator, as are ordinary products. GiNaC is capable of
+figuring out by itself which objects commutate and will group the factors
+by their class. Consider this example:
@example
...
- cout << "As method: " << sin(1).evalf() << endl;
- cout << "As function: " << evalf(sin(1)) << endl;
+ varidx mu(symbol("mu"), 4), nu(symbol("nu"), 4);
+ idx a(symbol("a"), 8), b(symbol("b"), 8);
+ ex e = -dirac_gamma(mu) * (2*color_T(a)) * 8 * color_T(b) * dirac_gamma(nu);
+ cout << e << endl;
+ // -> -16*(gamma~mu*gamma~nu)*(T.a*T.b)
...
@end example
-@cindex @code{subs()}
-The general rule is that wherever methods accept one or more parameters
-(@var{arg1}, @var{arg2}, @dots{}) the order of arguments the function
-wrapper accepts is the same but preceded by the object to act on
-(@var{object}, @var{arg1}, @var{arg2}, @dots{}). This approach is the
-most natural one in an OO model but it may lead to confusion for MapleV
-users because where they would type @code{A:=x+1; subs(x=2,A);} GiNaC
-would require @code{A=x+1; subs(A,x==2);} (after proper declaration of
-@code{A} and @code{x}). On the other hand, since MapleV returns 3 on
-@code{A:=x^2+3; coeff(A,x,0);} (GiNaC: @code{A=pow(x,2)+3;
-coeff(A,x,0);}) it is clear that MapleV is not trying to be consistent
-here. Also, users of MuPAD will in most cases feel more comfortable
-with GiNaC's convention. All function wrappers are implemented
-as simple inline functions which just call the corresponding method and
-are only provided for users uncomfortable with OO who are dead set to
-avoid method invocations. Generally, nested function wrappers are much
-harder to read than a sequence of methods and should therefore be
-avoided if possible. On the other hand, not everything in GiNaC is a
-method on class @code{ex} and sometimes calling a function cannot be
-avoided.
+As can be seen, GiNaC pulls out the overall commutative factor @samp{-16} and
+groups the non-commutative factors (the gammas and the su(3) generators)
+together while preserving the order of factors within each class (because
+Clifford objects commutate with color objects). The resulting expression is a
+@emph{commutative} product with two factors that are themselves non-commutative
+products (@samp{gamma~mu*gamma~nu} and @samp{T.a*T.b}). For clarification,
+parentheses are placed around the non-commutative products in the output.
-@menu
-* Information About Expressions::
-* Substituting Symbols::
-* Polynomial Arithmetic:: Working with polynomials.
-* Rational Expressions:: Working with rational functions.
-* Symbolic Differentiation::
-* Series Expansion:: Taylor and Laurent expansion.
-* Built-in Functions:: List of predefined mathematical functions.
-* Input/Output:: Input and output of expressions.
-@end menu
+@cindex @code{ncmul} (class)
+Non-commutative products are internally represented by objects of the class
+@code{ncmul}, as opposed to commutative products which are handled by the
+@code{mul} class. You will normally not have to worry about this distinction,
+though.
+The advantage of this approach is that you never have to worry about using
+(or forgetting to use) a special operator when constructing non-commutative
+expressions. Also, non-commutative products in GiNaC are more intelligent
+than in other computer algebra systems; they can, for example, automatically
+canonicalize themselves according to rules specified in the implementation
+of the non-commutative classes. The drawback is that to work with other than
+the built-in algebras you have to implement new classes yourself. Symbols
+always commutate and it's not possible to construct non-commutative products
+using symbols to represent the algebra elements or generators. User-defined
+functions can, however, be specified as being non-commutative.
-@node Information About Expressions, Substituting Symbols, Methods and Functions, Methods and Functions
-@c node-name, next, previous, up
-@section Getting information about expressions
+@cindex @code{return_type()}
+@cindex @code{return_type_tinfo()}
+Information about the commutativity of an object or expression can be
+obtained with the two member functions
-@subsection Checking expression types
-@cindex @code{is_ex_of_type()}
-@cindex @code{ex_to_numeric()}
-@cindex @code{ex_to_@dots{}}
-@cindex @code{Converting ex to other classes}
-@cindex @code{info()}
+@example
+unsigned ex::return_type() const;
+unsigned ex::return_type_tinfo() const;
+@end example
-Sometimes it's useful to check whether a given expression is a plain number,
-a sum, a polynomial with integer coefficients, or of some other specific type.
-GiNaC provides two functions for this (the first one is actually a macro):
+The @code{return_type()} function returns one of three values (defined in
+the header file @file{flags.h}), corresponding to three categories of
+expressions in GiNaC:
+
+@itemize
+@item @code{return_types::commutative}: Commutates with everything. Most GiNaC
+ classes are of this kind.
+@item @code{return_types::noncommutative}: Non-commutative, belonging to a
+ certain class of non-commutative objects which can be determined with the
+ @code{return_type_tinfo()} method. Expressions of this category commutate
+ with everything except @code{noncommutative} expressions of the same
+ class.
+@item @code{return_types::noncommutative_composite}: Non-commutative, composed
+ of non-commutative objects of different classes. Expressions of this
+ category don't commutate with any other @code{noncommutative} or
+ @code{noncommutative_composite} expressions.
+@end itemize
+
+The value returned by the @code{return_type_tinfo()} method is valid only
+when the return type of the expression is @code{noncommutative}. It is a
+value that is unique to the class of the object and usually one of the
+constants in @file{tinfos.h}, or derived therefrom.
+
+Here are a couple of examples:
+
+@cartouche
+@multitable @columnfractions 0.33 0.33 0.34
+@item @strong{Expression} @tab @strong{@code{return_type()}} @tab @strong{@code{return_type_tinfo()}}
+@item @code{42} @tab @code{commutative} @tab -
+@item @code{2*x-y} @tab @code{commutative} @tab -
+@item @code{dirac_ONE()} @tab @code{noncommutative} @tab @code{TINFO_clifford}
+@item @code{dirac_gamma(mu)*dirac_gamma(nu)} @tab @code{noncommutative} @tab @code{TINFO_clifford}
+@item @code{2*color_T(a)} @tab @code{noncommutative} @tab @code{TINFO_color}
+@item @code{dirac_ONE()*color_T(a)} @tab @code{noncommutative_composite} @tab -
+@end multitable
+@end cartouche
+
+Note: the @code{return_type_tinfo()} of Clifford objects is only equal to
+@code{TINFO_clifford} for objects with a representation label of zero.
+Other representation labels yield a different @code{return_type_tinfo()},
+but it's the same for any two objects with the same label. This is also true
+for color objects.
+
+A last note: With the exception of matrices, positive integer powers of
+non-commutative objects are automatically expanded in GiNaC. For example,
+@code{pow(a*b, 2)} becomes @samp{a*b*a*b} if @samp{a} and @samp{b} are
+non-commutative expressions).
+
+
+@cindex @code{clifford} (class)
+@subsection Clifford algebra
+
+@cindex @code{dirac_gamma()}
+Clifford algebra elements (also called Dirac gamma matrices, although GiNaC
+doesn't treat them as matrices) are designated as @samp{gamma~mu} and satisfy
+@samp{gamma~mu*gamma~nu + gamma~nu*gamma~mu = 2*eta~mu~nu} where @samp{eta~mu~nu}
+is the Minkowski metric tensor. Dirac gammas are constructed by the function
@example
-bool is_ex_of_type(const ex & e, TYPENAME t);
-bool ex::info(unsigned flag);
+ex dirac_gamma(const ex & mu, unsigned char rl = 0);
@end example
-When the test made by @code{is_ex_of_type()} returns true, it is safe to
-call one of the functions @code{ex_to_@dots{}}, where @code{@dots{}} is
-one of the class names (@xref{The Class Hierarchy}, for a list of all
-classes). For example, assuming @code{e} is an @code{ex}:
+which takes two arguments: the index and a @dfn{representation label} in the
+range 0 to 255 which is used to distinguish elements of different Clifford
+algebras (this is also called a @dfn{spin line index}). Gammas with different
+labels commutate with each other. The dimension of the index can be 4 or (in
+the framework of dimensional regularization) any symbolic value. Spinor
+indices on Dirac gammas are not supported in GiNaC.
+
+@cindex @code{dirac_ONE()}
+The unity element of a Clifford algebra is constructed by
@example
-@{
- @dots{}
- if (is_ex_of_type(e, numeric))
- numeric n = ex_to_numeric(e);
- @dots{}
-@}
+ex dirac_ONE(unsigned char rl = 0);
@end example
-@code{is_ex_of_type()} allows you to check whether the top-level object of
-an expression @samp{e} is an instance of the GiNaC class @samp{t}
-(@xref{The Class Hierarchy}, for a list of all classes). This is most useful,
-e.g., for checking whether an expression is a number, a sum, or a product:
+@strong{Note:} You must always use @code{dirac_ONE()} when referring to
+multiples of the unity element, even though it's customary to omit it.
+E.g. instead of @code{dirac_gamma(mu)*(dirac_slash(q,4)+m)} you have to
+write @code{dirac_gamma(mu)*(dirac_slash(q,4)+m*dirac_ONE())}. Otherwise,
+GiNaC will complain and/or produce incorrect results.
+
+@cindex @code{dirac_gamma5()}
+There is a special element @samp{gamma5} that commutates with all other
+gammas, has a unit square, and in 4 dimensions equals
+@samp{gamma~0 gamma~1 gamma~2 gamma~3}, provided by
+
+@example
+ex dirac_gamma5(unsigned char rl = 0);
+@end example
+
+@cindex @code{dirac_gammaL()}
+@cindex @code{dirac_gammaR()}
+The chiral projectors @samp{(1+/-gamma5)/2} are also available as proper
+objects, constructed by
+
+@example
+ex dirac_gammaL(unsigned char rl = 0);
+ex dirac_gammaR(unsigned char rl = 0);
+@end example
+
+They observe the relations @samp{gammaL^2 = gammaL}, @samp{gammaR^2 = gammaR},
+and @samp{gammaL gammaR = gammaR gammaL = 0}.
+
+@cindex @code{dirac_slash()}
+Finally, the function
+
+@example
+ex dirac_slash(const ex & e, const ex & dim, unsigned char rl = 0);
+@end example
+
+creates a term that represents a contraction of @samp{e} with the Dirac
+Lorentz vector (it behaves like a term of the form @samp{e.mu gamma~mu}
+with a unique index whose dimension is given by the @code{dim} argument).
+Such slashed expressions are printed with a trailing backslash, e.g. @samp{e\}.
+
+In products of dirac gammas, superfluous unity elements are automatically
+removed, squares are replaced by their values, and @samp{gamma5}, @samp{gammaL}
+and @samp{gammaR} are moved to the front.
+
+The @code{simplify_indexed()} function performs contractions in gamma strings,
+for example
@example
@{
- symbol x("x");
- ex e1 = 42;
- ex e2 = 4*x - 3;
- is_ex_of_type(e1, numeric); // true
- is_ex_of_type(e2, numeric); // false
- is_ex_of_type(e1, add); // false
- is_ex_of_type(e2, add); // true
- is_ex_of_type(e1, mul); // false
- is_ex_of_type(e2, mul); // false
+ ...
+ symbol a("a"), b("b"), D("D");
+ varidx mu(symbol("mu"), D);
+ ex e = dirac_gamma(mu) * dirac_slash(a, D)
+ * dirac_gamma(mu.toggle_variance());
+ cout << e << endl;
+ // -> gamma~mu*a\*gamma.mu
+ e = e.simplify_indexed();
+ cout << e << endl;
+ // -> -D*a\+2*a\
+ cout << e.subs(D == 4) << endl;
+ // -> -2*a\
+ ...
@}
@end example
-The @code{info()} method is used for checking certain attributes of
-expressions. The possible values for the @code{flag} argument are defined
-in @file{ginac/flags.h}, the most important being explained in the following
-table:
+@cindex @code{dirac_trace()}
+To calculate the trace of an expression containing strings of Dirac gammas
+you use one of the functions
-@cartouche
-@multitable @columnfractions .30 .70
+@example
+ex dirac_trace(const ex & e, const std::set<unsigned char> & rls, const ex & trONE = 4);
+ex dirac_trace(const ex & e, const lst & rll, const ex & trONE = 4);
+ex dirac_trace(const ex & e, unsigned char rl = 0, const ex & trONE = 4);
+@end example
+
+These functions take the trace over all gammas in the specified set @code{rls}
+or list @code{rll} of representation labels, or the single label @code{rl};
+gammas with other labels are left standing. The last argument to
+@code{dirac_trace()} is the value to be returned for the trace of the unity
+element, which defaults to 4.
+
+The @code{dirac_trace()} function is a linear functional that is equal to the
+ordinary matrix trace only in @math{D = 4} dimensions. In particular, the
+functional is not cyclic in @math{D != 4} dimensions when acting on
+expressions containing @samp{gamma5}, so it's not a proper trace. This
+@samp{gamma5} scheme is described in greater detail in
+@cite{The Role of gamma5 in Dimensional Regularization}.
+
+The value of the trace itself is also usually different in 4 and in
+@math{D != 4} dimensions:
+
+@example
+@{
+ // 4 dimensions
+ varidx mu(symbol("mu"), 4), nu(symbol("nu"), 4), rho(symbol("rho"), 4);
+ ex e = dirac_gamma(mu) * dirac_gamma(nu) *
+ dirac_gamma(mu.toggle_variance()) * dirac_gamma(rho);
+ cout << dirac_trace(e).simplify_indexed() << endl;
+ // -> -8*eta~rho~nu
+@}
+...
+@{
+ // D dimensions
+ symbol D("D");
+ varidx mu(symbol("mu"), D), nu(symbol("nu"), D), rho(symbol("rho"), D);
+ ex e = dirac_gamma(mu) * dirac_gamma(nu) *
+ dirac_gamma(mu.toggle_variance()) * dirac_gamma(rho);
+ cout << dirac_trace(e).simplify_indexed() << endl;
+ // -> 8*eta~rho~nu-4*eta~rho~nu*D
+@}
+@end example
+
+Here is an example for using @code{dirac_trace()} to compute a value that
+appears in the calculation of the one-loop vacuum polarization amplitude in
+QED:
+
+@example
+@{
+ symbol q("q"), l("l"), m("m"), ldotq("ldotq"), D("D");
+ varidx mu(symbol("mu"), D), nu(symbol("nu"), D);
+
+ scalar_products sp;
+ sp.add(l, l, pow(l, 2));
+ sp.add(l, q, ldotq);
+
+ ex e = dirac_gamma(mu) *
+ (dirac_slash(l, D) + dirac_slash(q, D) + m * dirac_ONE()) *
+ dirac_gamma(mu.toggle_variance()) *
+ (dirac_slash(l, D) + m * dirac_ONE());
+ e = dirac_trace(e).simplify_indexed(sp);
+ e = e.collect(lst(l, ldotq, m));
+ cout << e << endl;
+ // -> (8-4*D)*l^2+(8-4*D)*ldotq+4*D*m^2
+@}
+@end example
+
+The @code{canonicalize_clifford()} function reorders all gamma products that
+appear in an expression to a canonical (but not necessarily simple) form.
+You can use this to compare two expressions or for further simplifications:
+
+@example
+@{
+ varidx mu(symbol("mu"), 4), nu(symbol("nu"), 4);
+ ex e = dirac_gamma(mu) * dirac_gamma(nu) + dirac_gamma(nu) * dirac_gamma(mu);
+ cout << e << endl;
+ // -> gamma~mu*gamma~nu+gamma~nu*gamma~mu
+
+ e = canonicalize_clifford(e);
+ cout << e << endl;
+ // -> 2*ONE*eta~mu~nu
+@}
+@end example
+
+
+@cindex @code{color} (class)
+@subsection Color algebra
+
+@cindex @code{color_T()}
+For computations in quantum chromodynamics, GiNaC implements the base elements
+and structure constants of the su(3) Lie algebra (color algebra). The base
+elements @math{T_a} are constructed by the function
+
+@example
+ex color_T(const ex & a, unsigned char rl = 0);
+@end example
+
+which takes two arguments: the index and a @dfn{representation label} in the
+range 0 to 255 which is used to distinguish elements of different color
+algebras. Objects with different labels commutate with each other. The
+dimension of the index must be exactly 8 and it should be of class @code{idx},
+not @code{varidx}.
+
+@cindex @code{color_ONE()}
+The unity element of a color algebra is constructed by
+
+@example
+ex color_ONE(unsigned char rl = 0);
+@end example
+
+@strong{Note:} You must always use @code{color_ONE()} when referring to
+multiples of the unity element, even though it's customary to omit it.
+E.g. instead of @code{color_T(a)*(color_T(b)*indexed(X,b)+1)} you have to
+write @code{color_T(a)*(color_T(b)*indexed(X,b)+color_ONE())}. Otherwise,
+GiNaC may produce incorrect results.
+
+@cindex @code{color_d()}
+@cindex @code{color_f()}
+The functions
+
+@example
+ex color_d(const ex & a, const ex & b, const ex & c);
+ex color_f(const ex & a, const ex & b, const ex & c);
+@end example
+
+create the symmetric and antisymmetric structure constants @math{d_abc} and
+@math{f_abc} which satisfy @math{@{T_a, T_b@} = 1/3 delta_ab + d_abc T_c}
+and @math{[T_a, T_b] = i f_abc T_c}.
+
+@cindex @code{color_h()}
+There's an additional function
+
+@example
+ex color_h(const ex & a, const ex & b, const ex & c);
+@end example
+
+which returns the linear combination @samp{color_d(a, b, c)+I*color_f(a, b, c)}.
+
+The function @code{simplify_indexed()} performs some simplifications on
+expressions containing color objects:
+
+@example
+@{
+ ...
+ idx a(symbol("a"), 8), b(symbol("b"), 8), c(symbol("c"), 8),
+ k(symbol("k"), 8), l(symbol("l"), 8);
+
+ e = color_d(a, b, l) * color_f(a, b, k);
+ cout << e.simplify_indexed() << endl;
+ // -> 0
+
+ e = color_d(a, b, l) * color_d(a, b, k);
+ cout << e.simplify_indexed() << endl;
+ // -> 5/3*delta.k.l
+
+ e = color_f(l, a, b) * color_f(a, b, k);
+ cout << e.simplify_indexed() << endl;
+ // -> 3*delta.k.l
+
+ e = color_h(a, b, c) * color_h(a, b, c);
+ cout << e.simplify_indexed() << endl;
+ // -> -32/3
+
+ e = color_h(a, b, c) * color_T(b) * color_T(c);
+ cout << e.simplify_indexed() << endl;
+ // -> -2/3*T.a
+
+ e = color_h(a, b, c) * color_T(a) * color_T(b) * color_T(c);
+ cout << e.simplify_indexed() << endl;
+ // -> -8/9*ONE
+
+ e = color_T(k) * color_T(a) * color_T(b) * color_T(k);
+ cout << e.simplify_indexed() << endl;
+ // -> 1/4*delta.b.a*ONE-1/6*T.a*T.b
+ ...
+@end example
+
+@cindex @code{color_trace()}
+To calculate the trace of an expression containing color objects you use one
+of the functions
+
+@example
+ex color_trace(const ex & e, const std::set<unsigned char> & rls);
+ex color_trace(const ex & e, const lst & rll);
+ex color_trace(const ex & e, unsigned char rl = 0);
+@end example
+
+These functions take the trace over all color @samp{T} objects in the
+specified set @code{rls} or list @code{rll} of representation labels, or the
+single label @code{rl}; @samp{T}s with other labels are left standing. For
+example:
+
+@example
+ ...
+ e = color_trace(4 * color_T(a) * color_T(b) * color_T(c));
+ cout << e << endl;
+ // -> -I*f.a.c.b+d.a.c.b
+@}
+@end example
+
+
+@node Hash Maps, Methods and Functions, Non-commutative objects, Basic Concepts
+@c node-name, next, previous, up
+@section Hash Maps
+@cindex hash maps
+@cindex @code{exhashmap} (class)
+
+For your convenience, GiNaC offers the container template @code{exhashmap<T>}
+that can be used as a drop-in replacement for the STL
+@code{std::map<ex, T, ex_is_less>}, using hash tables to provide faster,
+typically constant-time, element look-up than @code{map<>}.
+
+@code{exhashmap<>} supports all @code{map<>} members and operations, with the
+following differences:
+
+@itemize @bullet
+@item
+no @code{lower_bound()} and @code{upper_bound()} methods
+@item
+no reverse iterators, no @code{rbegin()}/@code{rend()}
+@item
+no @code{operator<(exhashmap, exhashmap)}
+@item
+the comparison function object @code{key_compare} is hardcoded to
+@code{ex_is_less}
+@item
+the constructor @code{exhashmap(size_t n)} allows specifying the minimum
+initial hash table size (the actual table size after construction may be
+larger than the specified value)
+@item
+the method @code{size_t bucket_count()} returns the current size of the hash
+table
+@item
+@code{insert()} and @code{erase()} operations invalidate all iterators
+@end itemize
+
+
+@node Methods and Functions, Information About Expressions, Hash Maps, Top
+@c node-name, next, previous, up
+@chapter Methods and Functions
+@cindex polynomial
+
+In this chapter the most important algorithms provided by GiNaC will be
+described. Some of them are implemented as functions on expressions,
+others are implemented as methods provided by expression objects. If
+they are methods, there exists a wrapper function around it, so you can
+alternatively call it in a functional way as shown in the simple
+example:
+
+@example
+ ...
+ cout << "As method: " << sin(1).evalf() << endl;
+ cout << "As function: " << evalf(sin(1)) << endl;
+ ...
+@end example
+
+@cindex @code{subs()}
+The general rule is that wherever methods accept one or more parameters
+(@var{arg1}, @var{arg2}, @dots{}) the order of arguments the function
+wrapper accepts is the same but preceded by the object to act on
+(@var{object}, @var{arg1}, @var{arg2}, @dots{}). This approach is the
+most natural one in an OO model but it may lead to confusion for MapleV
+users because where they would type @code{A:=x+1; subs(x=2,A);} GiNaC
+would require @code{A=x+1; subs(A,x==2);} (after proper declaration of
+@code{A} and @code{x}). On the other hand, since MapleV returns 3 on
+@code{A:=x^2+3; coeff(A,x,0);} (GiNaC: @code{A=pow(x,2)+3;
+coeff(A,x,0);}) it is clear that MapleV is not trying to be consistent
+here. Also, users of MuPAD will in most cases feel more comfortable
+with GiNaC's convention. All function wrappers are implemented
+as simple inline functions which just call the corresponding method and
+are only provided for users uncomfortable with OO who are dead set to
+avoid method invocations. Generally, nested function wrappers are much
+harder to read than a sequence of methods and should therefore be
+avoided if possible. On the other hand, not everything in GiNaC is a
+method on class @code{ex} and sometimes calling a function cannot be
+avoided.
+
+@menu
+* Information About Expressions::
+* Numerical Evaluation::
+* Substituting Expressions::
+* Pattern Matching and Advanced Substitutions::
+* Applying a Function on Subexpressions::
+* Visitors and Tree Traversal::
+* Polynomial Arithmetic:: Working with polynomials.
+* Rational Expressions:: Working with rational functions.
+* Symbolic Differentiation::
+* Series Expansion:: Taylor and Laurent expansion.
+* Symmetrization::
+* Built-in Functions:: List of predefined mathematical functions.
+* Multiple polylogarithms::
+* Complex Conjugation::
+* Built-in Functions:: List of predefined mathematical functions.
+* Solving Linear Systems of Equations::
+* Input/Output:: Input and output of expressions.
+@end menu
+
+
+@node Information About Expressions, Numerical Evaluation, Methods and Functions, Methods and Functions
+@c node-name, next, previous, up
+@section Getting information about expressions
+
+@subsection Checking expression types
+@cindex @code{is_a<@dots{}>()}
+@cindex @code{is_exactly_a<@dots{}>()}
+@cindex @code{ex_to<@dots{}>()}
+@cindex Converting @code{ex} to other classes
+@cindex @code{info()}
+@cindex @code{return_type()}
+@cindex @code{return_type_tinfo()}
+
+Sometimes it's useful to check whether a given expression is a plain number,
+a sum, a polynomial with integer coefficients, or of some other specific type.
+GiNaC provides a couple of functions for this:
+
+@example
+bool is_a<T>(const ex & e);
+bool is_exactly_a<T>(const ex & e);
+bool ex::info(unsigned flag);
+unsigned ex::return_type() const;
+unsigned ex::return_type_tinfo() const;
+@end example
+
+When the test made by @code{is_a<T>()} returns true, it is safe to call
+one of the functions @code{ex_to<T>()}, where @code{T} is one of the
+class names (@xref{The Class Hierarchy}, for a list of all classes). For
+example, assuming @code{e} is an @code{ex}:
+
+@example
+@{
+ @dots{}
+ if (is_a<numeric>(e))
+ numeric n = ex_to<numeric>(e);
+ @dots{}
+@}
+@end example
+
+@code{is_a<T>(e)} allows you to check whether the top-level object of
+an expression @samp{e} is an instance of the GiNaC class @samp{T}
+(@xref{The Class Hierarchy}, for a list of all classes). This is most useful,
+e.g., for checking whether an expression is a number, a sum, or a product:
+
+@example
+@{
+ symbol x("x");
+ ex e1 = 42;
+ ex e2 = 4*x - 3;
+ is_a<numeric>(e1); // true
+ is_a<numeric>(e2); // false
+ is_a<add>(e1); // false
+ is_a<add>(e2); // true
+ is_a<mul>(e1); // false
+ is_a<mul>(e2); // false
+@}
+@end example
+
+In contrast, @code{is_exactly_a<T>(e)} allows you to check whether the
+top-level object of an expression @samp{e} is an instance of the GiNaC
+class @samp{T}, not including parent classes.
+
+The @code{info()} method is used for checking certain attributes of
+expressions. The possible values for the @code{flag} argument are defined
+in @file{ginac/flags.h}, the most important being explained in the following
+table:
+
+@cartouche
+@multitable @columnfractions .30 .70
@item @strong{Flag} @tab @strong{Returns true if the object is@dots{}}
@item @code{numeric}
-@tab @dots{}a number (same as @code{is_ex_of_type(..., numeric)})
+@tab @dots{}a number (same as @code{is_a<numeric>(...)})
@item @code{real}
@tab @dots{}a real integer, rational or float (i.e. is not complex)
@item @code{rational}
@item @code{prime}
@tab @dots{}a prime integer (probabilistic primality test)
@item @code{relation}
-@tab @dots{}a relation (same as @code{is_ex_of_type(..., relational)})
+@tab @dots{}a relation (same as @code{is_a<relational>(...)})
@item @code{relation_equal}
@tab @dots{}a @code{==} relation
@item @code{relation_not_equal}
@item @code{relation_greater_or_equal}
@tab @dots{}a @code{>=} relation
@item @code{symbol}
-@tab @dots{}a symbol (same as @code{is_ex_of_type(..., symbol)})
+@tab @dots{}a symbol (same as @code{is_a<symbol>(...)})
@item @code{list}
-@tab @dots{}a list (same as @code{is_ex_of_type(..., lst)})
+@tab @dots{}a list (same as @code{is_a<lst>(...)})
@item @code{polynomial}
@tab @dots{}a polynomial (i.e. only consists of sums and products of numbers and symbols with positive integer powers)
@item @code{integer_polynomial}
@end multitable
@end cartouche
+To determine whether an expression is commutative or non-commutative and if
+so, with which other expressions it would commutate, you use the methods
+@code{return_type()} and @code{return_type_tinfo()}. @xref{Non-commutative objects},
+for an explanation of these.
+
@subsection Accessing subexpressions
+@cindex container
+
+Many GiNaC classes, like @code{add}, @code{mul}, @code{lst}, and
+@code{function}, act as containers for subexpressions. For example, the
+subexpressions of a sum (an @code{add} object) are the individual terms,
+and the subexpressions of a @code{function} are the function's arguments.
+
@cindex @code{nops()}
@cindex @code{op()}
-@cindex @code{has()}
-@cindex container
-@cindex @code{relational} (class)
+GiNaC provides several ways of accessing subexpressions. The first way is to
+use the two methods
-GiNaC provides the two methods
+@example
+size_t ex::nops();
+ex ex::op(size_t i);
+@end example
+
+@code{nops()} determines the number of subexpressions (operands) contained
+in the expression, while @code{op(i)} returns the @code{i}-th
+(0..@code{nops()-1}) subexpression. In the case of a @code{power} object,
+@code{op(0)} will return the basis and @code{op(1)} the exponent. For
+@code{indexed} objects, @code{op(0)} is the base expression and @code{op(i)},
+@math{i>0} are the indices.
+
+@cindex iterators
+@cindex @code{const_iterator}
+The second way to access subexpressions is via the STL-style random-access
+iterator class @code{const_iterator} and the methods
@example
-unsigned ex::nops();
-ex ex::op(unsigned i);
+const_iterator ex::begin();
+const_iterator ex::end();
@end example
-for accessing the subexpressions in the container-like GiNaC classes like
-@code{add}, @code{mul}, @code{lst}, and @code{function}. @code{nops()}
-determines the number of subexpressions (@samp{operands}) contained, while
-@code{op()} returns the @code{i}-th (0..@code{nops()-1}) subexpression.
-In the case of a @code{power} object, @code{op(0)} will return the basis
-and @code{op(1)} the exponent. For @code{indexed} objects, @code{op(0)}
-is the base expression and @code{op(i)}, @math{i>0} are the indices.
+@code{begin()} returns an iterator referring to the first subexpression;
+@code{end()} returns an iterator which is one-past the last subexpression.
+If the expression has no subexpressions, then @code{begin() == end()}. These
+iterators can also be used in conjunction with non-modifying STL algorithms.
-The left-hand and right-hand side expressions of objects of class
-@code{relational} (and only of these) can also be accessed with the methods
+Here is an example that (non-recursively) prints the subexpressions of a
+given expression in three different ways:
@example
-ex ex::lhs();
-ex ex::rhs();
+@{
+ ex e = ...
+
+ // with nops()/op()
+ for (size_t i = 0; i != e.nops(); ++i)
+ cout << e.op(i) << endl;
+
+ // with iterators
+ for (const_iterator i = e.begin(); i != e.end(); ++i)
+ cout << *i << endl;
+
+ // with iterators and STL copy()
+ std::copy(e.begin(), e.end(), std::ostream_iterator<ex>(cout, "\n"));
+@}
+@end example
+
+@cindex @code{const_preorder_iterator}
+@cindex @code{const_postorder_iterator}
+@code{op()}/@code{nops()} and @code{const_iterator} only access an
+expression's immediate children. GiNaC provides two additional iterator
+classes, @code{const_preorder_iterator} and @code{const_postorder_iterator},
+that iterate over all objects in an expression tree, in preorder or postorder,
+respectively. They are STL-style forward iterators, and are created with the
+methods
+
+@example
+const_preorder_iterator ex::preorder_begin();
+const_preorder_iterator ex::preorder_end();
+const_postorder_iterator ex::postorder_begin();
+const_postorder_iterator ex::postorder_end();
@end example
-Finally, the method
+The following example illustrates the differences between
+@code{const_iterator}, @code{const_preorder_iterator}, and
+@code{const_postorder_iterator}:
@example
-bool ex::has(const ex & other);
+@{
+ symbol A("A"), B("B"), C("C");
+ ex e = lst(lst(A, B), C);
+
+ std::copy(e.begin(), e.end(),
+ std::ostream_iterator<ex>(cout, "\n"));
+ // @{A,B@}
+ // C
+
+ std::copy(e.preorder_begin(), e.preorder_end(),
+ std::ostream_iterator<ex>(cout, "\n"));
+ // @{@{A,B@},C@}
+ // @{A,B@}
+ // A
+ // B
+ // C
+
+ std::copy(e.postorder_begin(), e.postorder_end(),
+ std::ostream_iterator<ex>(cout, "\n"));
+ // A
+ // B
+ // @{A,B@}
+ // C
+ // @{@{A,B@},C@}
+@}
@end example
-checks whether an expression contains the given subexpression @code{other}.
-This only works reliably if @code{other} is of an atomic class such as a
-@code{numeric} or a @code{symbol}. It is, e.g., not possible to verify that
-@code{a+b+c} contains @code{a+c} (or @code{a+b}) as a subexpression.
+@cindex @code{relational} (class)
+Finally, the left-hand side and right-hand side expressions of objects of
+class @code{relational} (and only of these) can also be accessed with the
+methods
+
+@example
+ex ex::lhs();
+ex ex::rhs();
+@end example
@subsection Comparing expressions
@code{false}.
Actually, if you construct an expression like @code{a == b}, this will be
-represented by an object of the @code{relational} class (@xref{Relations}.)
-which is not evaluated until (explicitly or implicitely) cast to a @code{bool}.
+represented by an object of the @code{relational} class (@pxref{Relations})
+which is not evaluated until (explicitly or implicitly) cast to a @code{bool}.
There are also two methods
for checking whether one expression is equal to another, or equal to zero,
respectively.
-@strong{Warning:} You will also find an @code{ex::compare()} method in the
-GiNaC header files. This method is however only to be used internally by
-GiNaC to establish a canonical sort order for terms, and using it to compare
-expressions will give very surprising results.
+@subsection Ordering expressions
+@cindex @code{ex_is_less} (class)
+@cindex @code{ex_is_equal} (class)
+@cindex @code{compare()}
-@node Substituting Symbols, Polynomial Arithmetic, Information About Expressions, Methods and Functions
-@c node-name, next, previous, up
-@section Substituting symbols
-@cindex @code{subs()}
+Sometimes it is necessary to establish a mathematically well-defined ordering
+on a set of arbitrary expressions, for example to use expressions as keys
+in a @code{std::map<>} container, or to bring a vector of expressions into
+a canonical order (which is done internally by GiNaC for sums and products).
-Symbols can be replaced with expressions via the @code{.subs()} method:
+The operators @code{<}, @code{>} etc. described in the last section cannot
+be used for this, as they don't implement an ordering relation in the
+mathematical sense. In particular, they are not guaranteed to be
+antisymmetric: if @samp{a} and @samp{b} are different expressions, and
+@code{a < b} yields @code{false}, then @code{b < a} doesn't necessarily
+yield @code{true}.
+
+By default, STL classes and algorithms use the @code{<} and @code{==}
+operators to compare objects, which are unsuitable for expressions, but GiNaC
+provides two functors that can be supplied as proper binary comparison
+predicates to the STL:
@example
-ex ex::subs(const ex & e);
-ex ex::subs(const lst & syms, const lst & repls);
+class ex_is_less : public std::binary_function<ex, ex, bool> @{
+public:
+ bool operator()(const ex &lh, const ex &rh) const;
+@};
+
+class ex_is_equal : public std::binary_function<ex, ex, bool> @{
+public:
+ bool operator()(const ex &lh, const ex &rh) const;
+@};
@end example
-In the first form, @code{subs()} accepts a relational of the form
-@samp{symbol == expression} or a @code{lst} of such relationals. E.g.
+For example, to define a @code{map} that maps expressions to strings you
+have to use
@example
-@{
- symbol x("x"), y("y");
- ex e1 = 2*x^2-4*x+3;
- cout << "e1(7) = " << e1.subs(x == 7) << endl;
- ex e2 = x*y + x;
- cout << "e2(-2, 4) = " << e2.subs(lst(x == -2, y == 4)) << endl;
-@}
+std::map<ex, std::string, ex_is_less> myMap;
@end example
-will print @samp{73} and @samp{-10}, respectively.
+Omitting the @code{ex_is_less} template parameter will introduce spurious
+bugs because the map operates improperly.
-If you specify multiple substitutions, they are performed in parallel, so e.g.
-@code{subs(lst(x == y, y == x))} exchanges @samp{x} and @samp{y}.
+Other examples for the use of the functors:
-The second form of @code{subs()} takes two lists, one for the symbols and
-one for the expressions to be substituted (both lists must contain the same
-number of elements). Using this form, you would write @code{subs(lst(x, y), lst(y, x))}
-to exchange @samp{x} and @samp{y}.
+@example
+std::vector<ex> v;
+// fill vector
+...
+// sort vector
+std::sort(v.begin(), v.end(), ex_is_less());
-@node Polynomial Arithmetic, Rational Expressions, Substituting Symbols, Methods and Functions
-@c node-name, next, previous, up
-@section Polynomial arithmetic
+// count the number of expressions equal to '1'
+unsigned num_ones = std::count_if(v.begin(), v.end(),
+ std::bind2nd(ex_is_equal(), 1));
+@end example
-@subsection Expanding and collecting
-@cindex @code{expand()}
-@cindex @code{collect()}
+The implementation of @code{ex_is_less} uses the member function
-A polynomial in one or more variables has many equivalent
-representations. Some useful ones serve a specific purpose. Consider
-for example the trivariate polynomial @math{4*x*y + x*z + 20*y^2 +
-21*y*z + 4*z^2} (written down here in output-style). It is equivalent
-to the factorized polynomial @math{(x + 5*y + 4*z)*(4*y + z)}. Other
-representations are the recursive ones where one collects for exponents
-in one of the three variable. Since the factors are themselves
-polynomials in the remaining two variables the procedure can be
-repeated. In our expample, two possibilities would be @math{(4*y + z)*x
-+ 20*y^2 + 21*y*z + 4*z^2} and @math{20*y^2 + (21*z + 4*x)*y + 4*z^2 +
-x*z}.
+@example
+int ex::compare(const ex & other) const;
+@end example
-To bring an expression into expanded form, its method
+which returns @math{0} if @code{*this} and @code{other} are equal, @math{-1}
+if @code{*this} sorts before @code{other}, and @math{1} if @code{*this} sorts
+after @code{other}.
+
+
+@node Numerical Evaluation, Substituting Expressions, Information About Expressions, Methods and Functions
+@c node-name, next, previous, up
+@section Numerical Evaluation
+@cindex @code{evalf()}
+
+GiNaC keeps algebraic expressions, numbers and constants in their exact form.
+To evaluate them using floating-point arithmetic you need to call
@example
-ex ex::expand();
+ex ex::evalf(int level = 0) const;
@end example
-may be called. In our example above, this corresponds to @math{4*x*y +
-x*z + 20*y^2 + 21*y*z + 4*z^2}. Again, since the canonical form in
-GiNaC is not easily guessable you should be prepared to see different
-orderings of terms in such sums!
+@cindex @code{Digits}
+The accuracy of the evaluation is controlled by the global object @code{Digits}
+which can be assigned an integer value. The default value of @code{Digits}
+is 17. @xref{Numbers}, for more information and examples.
-Another useful representation of multivariate polynomials is as a
-univariate polynomial in one of the variables with the coefficients
-being polynomials in the remaining variables. The method
-@code{collect()} accomplishes this task:
+To evaluate an expression to a @code{double} floating-point number you can
+call @code{evalf()} followed by @code{numeric::to_double()}, like this:
@example
-ex ex::collect(const ex & s);
+@{
+ // Approximate sin(x/Pi)
+ symbol x("x");
+ ex e = series(sin(x/Pi), x == 0, 6);
+
+ // Evaluate numerically at x=0.1
+ ex f = evalf(e.subs(x == 0.1));
+
+ // ex_to<numeric> is an unsafe cast, so check the type first
+ if (is_a<numeric>(f)) @{
+ double d = ex_to<numeric>(f).to_double();
+ cout << d << endl;
+ // -> 0.0318256
+ @} else
+ // error
+@}
@end example
-Note that the original polynomial needs to be in expanded form in order
-to be able to find the coefficients properly.
-@subsection Degree and coefficients
-@cindex @code{degree()}
-@cindex @code{ldegree()}
-@cindex @code{coeff()}
+@node Substituting Expressions, Pattern Matching and Advanced Substitutions, Numerical Evaluation, Methods and Functions
+@c node-name, next, previous, up
+@section Substituting expressions
+@cindex @code{subs()}
-The degree and low degree of a polynomial can be obtained using the two
-methods
+Algebraic objects inside expressions can be replaced with arbitrary
+expressions via the @code{.subs()} method:
@example
-int ex::degree(const ex & s);
-int ex::ldegree(const ex & s);
+ex ex::subs(const ex & e, unsigned options = 0);
+ex ex::subs(const exmap & m, unsigned options = 0);
+ex ex::subs(const lst & syms, const lst & repls, unsigned options = 0);
@end example
-which also work reliably on non-expanded input polynomials (they even work
-on rational functions, returning the asymptotic degree). To extract
-a coefficient with a certain power from an expanded polynomial you use
+In the first form, @code{subs()} accepts a relational of the form
+@samp{object == expression} or a @code{lst} of such relationals:
@example
-ex ex::coeff(const ex & s, int n);
-@end example
+@{
+ symbol x("x"), y("y");
-You can also obtain the leading and trailing coefficients with the methods
+ ex e1 = 2*x^2-4*x+3;
+ cout << "e1(7) = " << e1.subs(x == 7) << endl;
+ // -> 73
-@example
-ex ex::lcoeff(const ex & s);
-ex ex::tcoeff(const ex & s);
+ ex e2 = x*y + x;
+ cout << "e2(-2, 4) = " << e2.subs(lst(x == -2, y == 4)) << endl;
+ // -> -10
+@}
@end example
-which are equivalent to @code{coeff(s, degree(s))} and @code{coeff(s, ldegree(s))},
-respectively.
+If you specify multiple substitutions, they are performed in parallel, so e.g.
+@code{subs(lst(x == y, y == x))} exchanges @samp{x} and @samp{y}.
-An application is illustrated in the next example, where a multivariate
-polynomial is analyzed:
+The second form of @code{subs()} takes an @code{exmap} object which is a
+pair associative container that maps expressions to expressions (currently
+implemented as a @code{std::map}). This is the most efficient one of the
+three @code{subs()} forms and should be used when the number of objects to
+be substituted is large or unknown.
-@example
-#include <ginac/ginac.h>
-using namespace std;
-using namespace GiNaC;
+Using this form, the second example from above would look like this:
-int main()
+@example
@{
symbol x("x"), y("y");
- ex PolyInp = 4*pow(x,3)*y + 5*x*pow(y,2) + 3*y
- - pow(x+y,2) + 2*pow(y+2,2) - 8;
- ex Poly = PolyInp.expand();
-
- for (int i=Poly.ldegree(x); i<=Poly.degree(x); ++i) @{
- cout << "The x^" << i << "-coefficient is "
- << Poly.coeff(x,i) << endl;
- @}
- cout << "As polynomial in y: "
- << Poly.collect(y) << endl;
+ ex e2 = x*y + x;
+
+ exmap m;
+ m[x] = -2;
+ m[y] = 4;
+ cout << "e2(-2, 4) = " << e2.subs(m) << endl;
@}
@end example
-When run, it returns an output in the following fashion:
+The third form of @code{subs()} takes two lists, one for the objects to be
+replaced and one for the expressions to be substituted (both lists must
+contain the same number of elements). Using this form, you would write
@example
-The x^0-coefficient is y^2+11*y
-The x^1-coefficient is 5*y^2-2*y
-The x^2-coefficient is -1
-The x^3-coefficient is 4*y
-As polynomial in y: -x^2+(5*x+1)*y^2+(-2*x+4*x^3+11)*y
+@{
+ symbol x("x"), y("y");
+ ex e2 = x*y + x;
+
+ cout << "e2(-2, 4) = " << e2.subs(lst(x, y), lst(-2, 4)) << endl;
+@}
@end example
-As always, the exact output may vary between different versions of GiNaC
-or even from run to run since the internal canonical ordering is not
-within the user's sphere of influence.
+The optional last argument to @code{subs()} is a combination of
+@code{subs_options} flags. There are two options available:
+@code{subs_options::no_pattern} disables pattern matching, which makes
+large @code{subs()} operations significantly faster if you are not using
+patterns. The second option, @code{subs_options::algebraic} enables
+algebraic substitutions in products and powers.
+@ref{Pattern Matching and Advanced Substitutions}, for more information
+about patterns and algebraic substitutions.
+@code{subs()} performs syntactic substitution of any complete algebraic
+object; it does not try to match sub-expressions as is demonstrated by the
+following example:
-@subsection Polynomial division
-@cindex polynomial division
-@cindex quotient
-@cindex remainder
-@cindex pseudo-remainder
-@cindex @code{quo()}
-@cindex @code{rem()}
-@cindex @code{prem()}
-@cindex @code{divide()}
+@example
+@{
+ symbol x("x"), y("y"), z("z");
-The two functions
+ ex e1 = pow(x+y, 2);
+ cout << e1.subs(x+y == 4) << endl;
+ // -> 16
-@example
-ex quo(const ex & a, const ex & b, const symbol & x);
-ex rem(const ex & a, const ex & b, const symbol & x);
+ ex e2 = sin(x)*sin(y)*cos(x);
+ cout << e2.subs(sin(x) == cos(x)) << endl;
+ // -> cos(x)^2*sin(y)
+
+ ex e3 = x+y+z;
+ cout << e3.subs(x+y == 4) << endl;
+ // -> x+y+z
+ // (and not 4+z as one might expect)
+@}
@end example
-compute the quotient and remainder of univariate polynomials in the variable
-@samp{x}. The results satisfy @math{a = b*quo(a, b, x) + rem(a, b, x)}.
+A more powerful form of substitution using wildcards is described in the
+next section.
-The additional function
+
+@node Pattern Matching and Advanced Substitutions, Applying a Function on Subexpressions, Substituting Expressions, Methods and Functions
+@c node-name, next, previous, up
+@section Pattern matching and advanced substitutions
+@cindex @code{wildcard} (class)
+@cindex Pattern matching
+
+GiNaC allows the use of patterns for checking whether an expression is of a
+certain form or contains subexpressions of a certain form, and for
+substituting expressions in a more general way.
+
+A @dfn{pattern} is an algebraic expression that optionally contains wildcards.
+A @dfn{wildcard} is a special kind of object (of class @code{wildcard}) that
+represents an arbitrary expression. Every wildcard has a @dfn{label} which is
+an unsigned integer number to allow having multiple different wildcards in a
+pattern. Wildcards are printed as @samp{$label} (this is also the way they
+are specified in @command{ginsh}). In C++ code, wildcard objects are created
+with the call
@example
-ex prem(const ex & a, const ex & b, const symbol & x);
+ex wild(unsigned label = 0);
@end example
-computes the pseudo-remainder of @samp{a} and @samp{b} which satisfies
-@math{c*a = b*q + prem(a, b, x)}, where @math{c = b.lcoeff(x) ^ (a.degree(x) - b.degree(x) + 1)}.
+which is simply a wrapper for the @code{wildcard()} constructor with a shorter
+name.
-Exact division of multivariate polynomials is performed by the function
+Some examples for patterns:
+
+@multitable @columnfractions .5 .5
+@item @strong{Constructed as} @tab @strong{Output as}
+@item @code{wild()} @tab @samp{$0}
+@item @code{pow(x,wild())} @tab @samp{x^$0}
+@item @code{atan2(wild(1),wild(2))} @tab @samp{atan2($1,$2)}
+@item @code{indexed(A,idx(wild(),3))} @tab @samp{A.$0}
+@end multitable
+
+Notes:
+
+@itemize
+@item Wildcards behave like symbols and are subject to the same algebraic
+ rules. E.g., @samp{$0+2*$0} is automatically transformed to @samp{3*$0}.
+@item As shown in the last example, to use wildcards for indices you have to
+ use them as the value of an @code{idx} object. This is because indices must
+ always be of class @code{idx} (or a subclass).
+@item Wildcards only represent expressions or subexpressions. It is not
+ possible to use them as placeholders for other properties like index
+ dimension or variance, representation labels, symmetry of indexed objects
+ etc.
+@item Because wildcards are commutative, it is not possible to use wildcards
+ as part of noncommutative products.
+@item A pattern does not have to contain wildcards. @samp{x} and @samp{x+y}
+ are also valid patterns.
+@end itemize
+
+@subsection Matching expressions
+@cindex @code{match()}
+The most basic application of patterns is to check whether an expression
+matches a given pattern. This is done by the function
@example
-bool divide(const ex & a, const ex & b, ex & q);
+bool ex::match(const ex & pattern);
+bool ex::match(const ex & pattern, lst & repls);
@end example
-If @samp{b} divides @samp{a} over the rationals, this function returns @code{true}
-and returns the quotient in the variable @code{q}. Otherwise it returns @code{false}
-in which case the value of @code{q} is undefined.
+This function returns @code{true} when the expression matches the pattern
+and @code{false} if it doesn't. If used in the second form, the actual
+subexpressions matched by the wildcards get returned in the @code{repls}
+object as a list of relations of the form @samp{wildcard == expression}.
+If @code{match()} returns false, the state of @code{repls} is undefined.
+For reproducible results, the list should be empty when passed to
+@code{match()}, but it is also possible to find similarities in multiple
+expressions by passing in the result of a previous match.
+The matching algorithm works as follows:
-@subsection Unit, content and primitive part
-@cindex @code{unit()}
-@cindex @code{content()}
-@cindex @code{primpart()}
+@itemize
+@item A single wildcard matches any expression. If one wildcard appears
+ multiple times in a pattern, it must match the same expression in all
+ places (e.g. @samp{$0} matches anything, and @samp{$0*($0+1)} matches
+ @samp{x*(x+1)} but not @samp{x*(y+1)}).
+@item If the expression is not of the same class as the pattern, the match
+ fails (i.e. a sum only matches a sum, a function only matches a function,
+ etc.).
+@item If the pattern is a function, it only matches the same function
+ (i.e. @samp{sin($0)} matches @samp{sin(x)} but doesn't match @samp{exp(x)}).
+@item Except for sums and products, the match fails if the number of
+ subexpressions (@code{nops()}) is not equal to the number of subexpressions
+ of the pattern.
+@item If there are no subexpressions, the expressions and the pattern must
+ be equal (in the sense of @code{is_equal()}).
+@item Except for sums and products, each subexpression (@code{op()}) must
+ match the corresponding subexpression of the pattern.
+@end itemize
-The methods
+Sums (@code{add}) and products (@code{mul}) are treated in a special way to
+account for their commutativity and associativity:
+
+@itemize
+@item If the pattern contains a term or factor that is a single wildcard,
+ this one is used as the @dfn{global wildcard}. If there is more than one
+ such wildcard, one of them is chosen as the global wildcard in a random
+ way.
+@item Every term/factor of the pattern, except the global wildcard, is
+ matched against every term of the expression in sequence. If no match is
+ found, the whole match fails. Terms that did match are not considered in
+ further matches.
+@item If there are no unmatched terms left, the match succeeds. Otherwise
+ the match fails unless there is a global wildcard in the pattern, in
+ which case this wildcard matches the remaining terms.
+@end itemize
+
+In general, having more than one single wildcard as a term of a sum or a
+factor of a product (such as @samp{a+$0+$1}) will lead to unpredictable or
+ambiguous results.
+
+Here are some examples in @command{ginsh} to demonstrate how it works (the
+@code{match()} function in @command{ginsh} returns @samp{FAIL} if the
+match fails, and the list of wildcard replacements otherwise):
+
+@example
+> match((x+y)^a,(x+y)^a);
+@{@}
+> match((x+y)^a,(x+y)^b);
+FAIL
+> match((x+y)^a,$1^$2);
+@{$1==x+y,$2==a@}
+> match((x+y)^a,$1^$1);
+FAIL
+> match((x+y)^(x+y),$1^$1);
+@{$1==x+y@}
+> match((x+y)^(x+y),$1^$2);
+@{$1==x+y,$2==x+y@}
+> match((a+b)*(a+c),($1+b)*($1+c));
+@{$1==a@}
+> match((a+b)*(a+c),(a+$1)*(a+$2));
+@{$1==c,$2==b@}
+ (Unpredictable. The result might also be [$1==c,$2==b].)
+> match((a+b)*(a+c),($1+$2)*($1+$3));
+ (The result is undefined. Due to the sequential nature of the algorithm
+ and the re-ordering of terms in GiNaC, the match for the first factor
+ may be @{$1==a,$2==b@} in which case the match for the second factor
+ succeeds, or it may be @{$1==b,$2==a@} which causes the second match to
+ fail.)
+> match(a*(x+y)+a*z+b,a*$1+$2);
+ (This is also ambiguous and may return either @{$1==z,$2==a*(x+y)+b@} or
+ @{$1=x+y,$2=a*z+b@}.)
+> match(a+b+c+d+e+f,c);
+FAIL
+> match(a+b+c+d+e+f,c+$0);
+@{$0==a+e+b+f+d@}
+> match(a+b+c+d+e+f,c+e+$0);
+@{$0==a+b+f+d@}
+> match(a+b,a+b+$0);
+@{$0==0@}
+> match(a*b^2,a^$1*b^$2);
+FAIL
+ (The matching is syntactic, not algebraic, and "a" doesn't match "a^$1"
+ even though a==a^1.)
+> match(x*atan2(x,x^2),$0*atan2($0,$0^2));
+@{$0==x@}
+> match(atan2(y,x^2),atan2(y,$0));
+@{$0==x^2@}
+@end example
+
+@subsection Matching parts of expressions
+@cindex @code{has()}
+A more general way to look for patterns in expressions is provided by the
+member function
@example
-ex ex::unit(const symbol & x);
-ex ex::content(const symbol & x);
-ex ex::primpart(const symbol & x);
+bool ex::has(const ex & pattern);
@end example
-return the unit part, content part, and primitive polynomial of a multivariate
-polynomial with respect to the variable @samp{x} (the unit part being the sign
-of the leading coefficient, the content part being the GCD of the coefficients,
-and the primitive polynomial being the input polynomial divided by the unit and
-content parts). The product of unit, content, and primitive part is the
-original polynomial.
+This function checks whether a pattern is matched by an expression itself or
+by any of its subexpressions.
+Again some examples in @command{ginsh} for illustration (in @command{ginsh},
+@code{has()} returns @samp{1} for @code{true} and @samp{0} for @code{false}):
-@subsection GCD and LCM
-@cindex GCD
-@cindex LCM
-@cindex @code{gcd()}
-@cindex @code{lcm()}
+@example
+> has(x*sin(x+y+2*a),y);
+1
+> has(x*sin(x+y+2*a),x+y);
+0
+ (This is because in GiNaC, "x+y" is not a subexpression of "x+y+2*a" (which
+ has the subexpressions "x", "y" and "2*a".)
+> has(x*sin(x+y+2*a),x+y+$1);
+1
+ (But this is possible.)
+> has(x*sin(2*(x+y)+2*a),x+y);
+0
+ (This fails because "2*(x+y)" automatically gets converted to "2*x+2*y" of
+ which "x+y" is not a subexpression.)
+> has(x+1,x^$1);
+0
+ (Although x^1==x and x^0==1, neither "x" nor "1" are actually of the form
+ "x^something".)
+> has(4*x^2-x+3,$1*x);
+1
+> has(4*x^2+x+3,$1*x);
+0
+ (Another possible pitfall. The first expression matches because the term
+ "-x" has the form "(-1)*x" in GiNaC. To check whether a polynomial
+ contains a linear term you should use the coeff() function instead.)
+@end example
-The functions for polynomial greatest common divisor and least common
-multiple have the synopsis
+@cindex @code{find()}
+The method
@example
-ex gcd(const ex & a, const ex & b);
-ex lcm(const ex & a, const ex & b);
+bool ex::find(const ex & pattern, lst & found);
@end example
-The functions @code{gcd()} and @code{lcm()} accept two expressions
-@code{a} and @code{b} as arguments and return a new expression, their
-greatest common divisor or least common multiple, respectively. If the
-polynomials @code{a} and @code{b} are coprime @code{gcd(a,b)} returns 1
-and @code{lcm(a,b)} returns the product of @code{a} and @code{b}.
+works a bit like @code{has()} but it doesn't stop upon finding the first
+match. Instead, it appends all found matches to the specified list. If there
+are multiple occurrences of the same expression, it is entered only once to
+the list. @code{find()} returns false if no matches were found (in
+@command{ginsh}, it returns an empty list):
@example
-#include <ginac/ginac.h>
-using namespace GiNaC;
+> find(1+x+x^2+x^3,x);
+@{x@}
+> find(1+x+x^2+x^3,y);
+@{@}
+> find(1+x+x^2+x^3,x^$1);
+@{x^3,x^2@}
+ (Note the absence of "x".)
+> expand((sin(x)+sin(y))*(a+b));
+sin(y)*a+sin(x)*b+sin(x)*a+sin(y)*b
+> find(%,sin($1));
+@{sin(y),sin(x)@}
+@end example
-int main()
-@{
- symbol x("x"), y("y"), z("z");
- ex P_a = 4*x*y + x*z + 20*pow(y, 2) + 21*y*z + 4*pow(z, 2);
- ex P_b = x*y + 3*x*z + 5*pow(y, 2) + 19*y*z + 12*pow(z, 2);
+@subsection Substituting expressions
+@cindex @code{subs()}
+Probably the most useful application of patterns is to use them for
+substituting expressions with the @code{subs()} method. Wildcards can be
+used in the search patterns as well as in the replacement expressions, where
+they get replaced by the expressions matched by them. @code{subs()} doesn't
+know anything about algebra; it performs purely syntactic substitutions.
+
+Some examples:
+
+@example
+> subs(a^2+b^2+(x+y)^2,$1^2==$1^3);
+b^3+a^3+(x+y)^3
+> subs(a^4+b^4+(x+y)^4,$1^2==$1^3);
+b^4+a^4+(x+y)^4
+> subs((a+b+c)^2,a+b==x);
+(a+b+c)^2
+> subs((a+b+c)^2,a+b+$1==x+$1);
+(x+c)^2
+> subs(a+2*b,a+b==x);
+a+2*b
+> subs(4*x^3-2*x^2+5*x-1,x==a);
+-1+5*a-2*a^2+4*a^3
+> subs(4*x^3-2*x^2+5*x-1,x^$0==a^$0);
+-1+5*x-2*a^2+4*a^3
+> subs(sin(1+sin(x)),sin($1)==cos($1));
+cos(1+cos(x))
+> expand(subs(a*sin(x+y)^2+a*cos(x+y)^2+b,cos($1)^2==1-sin($1)^2));
+a+b
+@end example
+
+The last example would be written in C++ in this way:
- ex P_gcd = gcd(P_a, P_b);
- // x + 5*y + 4*z
- ex P_lcm = lcm(P_a, P_b);
- // 4*x*y^2 + 13*y*x*z + 20*y^3 + 81*y^2*z + 67*y*z^2 + 3*x*z^2 + 12*z^3
+@example
+@{
+ symbol a("a"), b("b"), x("x"), y("y");
+ e = a*pow(sin(x+y), 2) + a*pow(cos(x+y), 2) + b;
+ e = e.subs(pow(cos(wild()), 2) == 1-pow(sin(wild()), 2));
+ cout << e.expand() << endl;
+ // -> a+b
@}
@end example
+@subsection Algebraic substitutions
+Supplying the @code{subs_options::algebraic} option to @code{subs()}
+enables smarter, algebraic substitutions in products and powers. If you want
+to substitute some factors of a product, you only need to list these factors
+in your pattern. Furthermore, if an (integer) power of some expression occurs
+in your pattern and in the expression that you want the substitution to occur
+in, it can be substituted as many times as possible, without getting negative
+powers.
-@subsection Square-free decomposition
-@cindex square-free decomposition
-@cindex factorization
-@cindex @code{sqrfree()}
+An example clarifies it all (hopefully):
-GiNaC still lacks proper factorization support. Some form of
-factorization is, however, easily implemented by noting that factors
-appearing in a polynomial with power two or more also appear in the
-derivative and hence can easily be found by computing the GCD of the
-original polynomial and its derivatives. Any system has an interface
-for this so called square-free factorization. So we provide one, too:
@example
-ex sqrfree(const ex & a, const lst & l = lst());
-@end example
-Here is an example that by the way illustrates how the result may depend
-on the order of differentiation:
-@example
- ...
- symbol x("x"), y("y");
- ex BiVarPol = expand(pow(x-2*y*x,3) * pow(x+y,2) * (x-y));
+cout << (a*a*a*a+b*b*b*b+pow(x+y,4)).subs(wild()*wild()==pow(wild(),3),
+ subs_options::algebraic) << endl;
+// --> (y+x)^6+b^6+a^6
- cout << sqrfree(BiVarPol, lst(x,y)) << endl;
- // -> (y+x)^2*(-1+6*y+8*y^3-12*y^2)*(y-x)*x^3
+cout << ((a+b+c)*(a+b+c)).subs(a+b==x,subs_options::algebraic) << endl;
+// --> (c+b+a)^2
+// Powers and products are smart, but addition is just the same.
- cout << sqrfree(BiVarPol, lst(y,x)) << endl;
- // -> (1-2*y)^3*(y+x)^2*(-y+x)*x^3
+cout << ((a+b+c)*(a+b+c)).subs(a+b+wild()==x+wild(), subs_options::algebraic)
+ << endl;
+// --> (x+c)^2
+// As I said: addition is just the same.
- cout << sqrfree(BiVarPol) << endl;
- // -> depending on luck, any of the above
- ...
-@end example
+cout << (pow(a,5)*pow(b,7)+2*b).subs(b*b*a==x,subs_options::algebraic) << endl;
+// --> x^3*b*a^2+2*b
+cout << (pow(a,-5)*pow(b,-7)+2*b).subs(1/(b*b*a)==x,subs_options::algebraic)
+ << endl;
+// --> 2*b+x^3*b^(-1)*a^(-2)
-@node Rational Expressions, Symbolic Differentiation, Polynomial Arithmetic, Methods and Functions
-@c node-name, next, previous, up
-@section Rational expressions
+cout << (4*x*x*x-2*x*x+5*x-1).subs(x==a,subs_options::algebraic) << endl;
+// --> -1-2*a^2+4*a^3+5*a
-@subsection The @code{normal} method
-@cindex @code{normal()}
-@cindex simplification
-@cindex temporary replacement
+cout << (4*x*x*x-2*x*x+5*x-1).subs(pow(x,wild())==pow(a,wild()),
+ subs_options::algebraic) << endl;
+// --> -1+5*x+4*x^3-2*x^2
+// You should not really need this kind of patterns very often now.
+// But perhaps this it's-not-a-bug-it's-a-feature (c/sh)ould still change.
-Some basic form of simplification of expressions is called for frequently.
-GiNaC provides the method @code{.normal()}, which converts a rational function
-into an equivalent rational function of the form @samp{numerator/denominator}
-where numerator and denominator are coprime. If the input expression is already
-a fraction, it just finds the GCD of numerator and denominator and cancels it,
-otherwise it performs fraction addition and multiplication.
+cout << ex(sin(1+sin(x))).subs(sin(wild())==cos(wild()),
+ subs_options::algebraic) << endl;
+// --> cos(1+cos(x))
-@code{.normal()} can also be used on expressions which are not rational functions
-as it will replace all non-rational objects (like functions or non-integer
-powers) by temporary symbols to bring the expression to the domain of rational
-functions before performing the normalization, and re-substituting these
-symbols afterwards. This algorithm is also available as a separate method
-@code{.to_rational()}, described below.
+cout << expand((a*sin(x+y)*sin(x+y)+a*cos(x+y)*cos(x+y)+b)
+ .subs((pow(cos(wild()),2)==1-pow(sin(wild()),2)),
+ subs_options::algebraic)) << endl;
+// --> b+a
+@end example
-This means that both expressions @code{t1} and @code{t2} are indeed
-simplified in this little program:
-@example
-#include <ginac/ginac.h>
-using namespace GiNaC;
+@node Applying a Function on Subexpressions, Visitors and Tree Traversal, Pattern Matching and Advanced Substitutions, Methods and Functions
+@c node-name, next, previous, up
+@section Applying a Function on Subexpressions
+@cindex tree traversal
+@cindex @code{map()}
-int main()
+Sometimes you may want to perform an operation on specific parts of an
+expression while leaving the general structure of it intact. An example
+of this would be a matrix trace operation: the trace of a sum is the sum
+of the traces of the individual terms. That is, the trace should @dfn{map}
+on the sum, by applying itself to each of the sum's operands. It is possible
+to do this manually which usually results in code like this:
+
+@example
+ex calc_trace(ex e)
@{
- symbol x("x");
- ex t1 = (pow(x,2) + 2*x + 1)/(x + 1);
- ex t2 = (pow(sin(x),2) + 2*sin(x) + 1)/(sin(x) + 1);
- std::cout << "t1 is " << t1.normal() << std::endl;
- std::cout << "t2 is " << t2.normal() << std::endl;
+ if (is_a<matrix>(e))
+ return ex_to<matrix>(e).trace();
+ else if (is_a<add>(e)) @{
+ ex sum = 0;
+ for (size_t i=0; i<e.nops(); i++)
+ sum += calc_trace(e.op(i));
+ return sum;
+ @} else if (is_a<mul>)(e)) @{
+ ...
+ @} else @{
+ ...
+ @}
@}
@end example
-Of course this works for multivariate polynomials too, so the ratio of
-the sample-polynomials from the section about GCD and LCM above would be
-normalized to @code{P_a/P_b} = @code{(4*y+z)/(y+3*z)}.
-
-
-@subsection Numerator and denominator
-@cindex numerator
-@cindex denominator
-@cindex @code{numer()}
-@cindex @code{denom()}
+This is, however, slightly inefficient (if the sum is very large it can take
+a long time to add the terms one-by-one), and its applicability is limited to
+a rather small class of expressions. If @code{calc_trace()} is called with
+a relation or a list as its argument, you will probably want the trace to
+be taken on both sides of the relation or of all elements of the list.
-The numerator and denominator of an expression can be obtained with
+GiNaC offers the @code{map()} method to aid in the implementation of such
+operations:
@example
-ex ex::numer();
-ex ex::denom();
+ex ex::map(map_function & f) const;
+ex ex::map(ex (*f)(const ex & e)) const;
@end example
-These functions will first normalize the expression as described above and
-then return the numerator or denominator, respectively.
+In the first (preferred) form, @code{map()} takes a function object that
+is subclassed from the @code{map_function} class. In the second form, it
+takes a pointer to a function that accepts and returns an expression.
+@code{map()} constructs a new expression of the same type, applying the
+specified function on all subexpressions (in the sense of @code{op()}),
+non-recursively.
+The use of a function object makes it possible to supply more arguments to
+the function that is being mapped, or to keep local state information.
+The @code{map_function} class declares a virtual function call operator
+that you can overload. Here is a sample implementation of @code{calc_trace()}
+that uses @code{map()} in a recursive fashion:
-@subsection Converting to a rational expression
-@cindex @code{to_rational()}
+@example
+struct calc_trace : public map_function @{
+ ex operator()(const ex &e)
+ @{
+ if (is_a<matrix>(e))
+ return ex_to<matrix>(e).trace();
+ else if (is_a<mul>(e)) @{
+ ...
+ @} else
+ return e.map(*this);
+ @}
+@};
+@end example
-Some of the methods described so far only work on polynomials or rational
-functions. GiNaC provides a way to extend the domain of these functions to
-general expressions by using the temporary replacement algorithm described
-above. You do this by calling
+This function object could then be used like this:
@example
-ex ex::to_rational(lst &l);
+@{
+ ex M = ... // expression with matrices
+ calc_trace do_trace;
+ ex tr = do_trace(M);
+@}
@end example
-on the expression to be converted. The supplied @code{lst} will be filled
-with the generated temporary symbols and their replacement expressions in
-a format that can be used directly for the @code{subs()} method. It can also
-already contain a list of replacements from an earlier application of
-@code{.to_rational()}, so it's possible to use it on multiple expressions
-and get consistent results.
-
-For example,
+Here is another example for you to meditate over. It removes quadratic
+terms in a variable from an expanded polynomial:
@example
-@{
+struct map_rem_quad : public map_function @{
+ ex var;
+ map_rem_quad(const ex & var_) : var(var_) @{@}
+
+ ex operator()(const ex & e)
+ @{
+ if (is_a<add>(e) || is_a<mul>(e))
+ return e.map(*this);
+ else if (is_a<power>(e) &&
+ e.op(0).is_equal(var) && e.op(1).info(info_flags::even))
+ return 0;
+ else
+ return e;
+ @}
+@};
+
+...
+
+@{
+ symbol x("x"), y("y");
+
+ ex e;
+ for (int i=0; i<8; i++)
+ e += pow(x, i) * pow(y, 8-i) * (i+1);
+ cout << e << endl;
+ // -> 4*y^5*x^3+5*y^4*x^4+8*y*x^7+7*y^2*x^6+2*y^7*x+6*y^3*x^5+3*y^6*x^2+y^8
+
+ map_rem_quad rem_quad(x);
+ cout << rem_quad(e) << endl;
+ // -> 4*y^5*x^3+8*y*x^7+2*y^7*x+6*y^3*x^5+y^8
+@}
+@end example
+
+@command{ginsh} offers a slightly different implementation of @code{map()}
+that allows applying algebraic functions to operands. The second argument
+to @code{map()} is an expression containing the wildcard @samp{$0} which
+acts as the placeholder for the operands:
+
+@example
+> map(a*b,sin($0));
+sin(a)*sin(b)
+> map(a+2*b,sin($0));
+sin(a)+sin(2*b)
+> map(@{a,b,c@},$0^2+$0);
+@{a^2+a,b^2+b,c^2+c@}
+@end example
+
+Note that it is only possible to use algebraic functions in the second
+argument. You can not use functions like @samp{diff()}, @samp{op()},
+@samp{subs()} etc. because these are evaluated immediately:
+
+@example
+> map(@{a,b,c@},diff($0,a));
+@{0,0,0@}
+ This is because "diff($0,a)" evaluates to "0", so the command is equivalent
+ to "map(@{a,b,c@},0)".
+@end example
+
+
+@node Visitors and Tree Traversal, Polynomial Arithmetic, Applying a Function on Subexpressions, Methods and Functions
+@c node-name, next, previous, up
+@section Visitors and Tree Traversal
+@cindex tree traversal
+@cindex @code{visitor} (class)
+@cindex @code{accept()}
+@cindex @code{visit()}
+@cindex @code{traverse()}
+@cindex @code{traverse_preorder()}
+@cindex @code{traverse_postorder()}
+
+Suppose that you need a function that returns a list of all indices appearing
+in an arbitrary expression. The indices can have any dimension, and for
+indices with variance you always want the covariant version returned.
+
+You can't use @code{get_free_indices()} because you also want to include
+dummy indices in the list, and you can't use @code{find()} as it needs
+specific index dimensions (and it would require two passes: one for indices
+with variance, one for plain ones).
+
+The obvious solution to this problem is a tree traversal with a type switch,
+such as the following:
+
+@example
+void gather_indices_helper(const ex & e, lst & l)
+@{
+ if (is_a<varidx>(e)) @{
+ const varidx & vi = ex_to<varidx>(e);
+ l.append(vi.is_covariant() ? vi : vi.toggle_variance());
+ @} else if (is_a<idx>(e)) @{
+ l.append(e);
+ @} else @{
+ size_t n = e.nops();
+ for (size_t i = 0; i < n; ++i)
+ gather_indices_helper(e.op(i), l);
+ @}
+@}
+
+lst gather_indices(const ex & e)
+@{
+ lst l;
+ gather_indices_helper(e, l);
+ l.sort();
+ l.unique();
+ return l;
+@}
+@end example
+
+This works fine but fans of object-oriented programming will feel
+uncomfortable with the type switch. One reason is that there is a possibility
+for subtle bugs regarding derived classes. If we had, for example, written
+
+@example
+ if (is_a<idx>(e)) @{
+ ...
+ @} else if (is_a<varidx>(e)) @{
+ ...
+@end example
+
+in @code{gather_indices_helper}, the code wouldn't have worked because the
+first line "absorbs" all classes derived from @code{idx}, including
+@code{varidx}, so the special case for @code{varidx} would never have been
+executed.
+
+Also, for a large number of classes, a type switch like the above can get
+unwieldy and inefficient (it's a linear search, after all).
+@code{gather_indices_helper} only checks for two classes, but if you had to
+write a function that required a different implementation for nearly
+every GiNaC class, the result would be very hard to maintain and extend.
+
+The cleanest approach to the problem would be to add a new virtual function
+to GiNaC's class hierarchy. In our example, there would be specializations
+for @code{idx} and @code{varidx} while the default implementation in
+@code{basic} performed the tree traversal. Unfortunately, in C++ it's
+impossible to add virtual member functions to existing classes without
+changing their source and recompiling everything. GiNaC comes with source,
+so you could actually do this, but for a small algorithm like the one
+presented this would be impractical.
+
+One solution to this dilemma is the @dfn{Visitor} design pattern,
+which is implemented in GiNaC (actually, Robert Martin's Acyclic Visitor
+variation, described in detail in
+@uref{http://objectmentor.com/publications/acv.pdf}). Instead of adding
+virtual functions to the class hierarchy to implement operations, GiNaC
+provides a single "bouncing" method @code{accept()} that takes an instance
+of a special @code{visitor} class and redirects execution to the one
+@code{visit()} virtual function of the visitor that matches the type of
+object that @code{accept()} was being invoked on.
+
+Visitors in GiNaC must derive from the global @code{visitor} class as well
+as from the class @code{T::visitor} of each class @code{T} they want to
+visit, and implement the member functions @code{void visit(const T &)} for
+each class.
+
+A call of
+
+@example
+void ex::accept(visitor & v) const;
+@end example
+
+will then dispatch to the correct @code{visit()} member function of the
+specified visitor @code{v} for the type of GiNaC object at the root of the
+expression tree (e.g. a @code{symbol}, an @code{idx} or a @code{mul}).
+
+Here is an example of a visitor:
+
+@example
+class my_visitor
+ : public visitor, // this is required
+ public add::visitor, // visit add objects
+ public numeric::visitor, // visit numeric objects
+ public basic::visitor // visit basic objects
+@{
+ void visit(const add & x)
+ @{ cout << "called with an add object" << endl; @}
+
+ void visit(const numeric & x)
+ @{ cout << "called with a numeric object" << endl; @}
+
+ void visit(const basic & x)
+ @{ cout << "called with a basic object" << endl; @}
+@};
+@end example
+
+which can be used as follows:
+
+@example
+...
symbol x("x");
- ex a = pow(sin(x), 2) - pow(cos(x), 2);
- ex b = sin(x) + cos(x);
- ex q;
+ ex e1 = 42;
+ ex e2 = 4*x-3;
+ ex e3 = 8*x;
+
+ my_visitor v;
+ e1.accept(v);
+ // prints "called with a numeric object"
+ e2.accept(v);
+ // prints "called with an add object"
+ e3.accept(v);
+ // prints "called with a basic object"
+...
+@end example
+
+The @code{visit(const basic &)} method gets called for all objects that are
+not @code{numeric} or @code{add} and acts as an (optional) default.
+
+From a conceptual point of view, the @code{visit()} methods of the visitor
+behave like a newly added virtual function of the visited hierarchy.
+In addition, visitors can store state in member variables, and they can
+be extended by deriving a new visitor from an existing one, thus building
+hierarchies of visitors.
+
+We can now rewrite our index example from above with a visitor:
+
+@example
+class gather_indices_visitor
+ : public visitor, public idx::visitor, public varidx::visitor
+@{
lst l;
- divide(a.to_rational(l), b.to_rational(l), q);
- cout << q.subs(l) << endl;
+
+ void visit(const idx & i)
+ @{
+ l.append(i);
+ @}
+
+ void visit(const varidx & vi)
+ @{
+ l.append(vi.is_covariant() ? vi : vi.toggle_variance());
+ @}
+
+public:
+ const lst & get_result() // utility function
+ @{
+ l.sort();
+ l.unique();
+ return l;
+ @}
+@};
+@end example
+
+What's missing is the tree traversal. We could implement it in
+@code{visit(const basic &)}, but GiNaC has predefined methods for this:
+
+@example
+void ex::traverse_preorder(visitor & v) const;
+void ex::traverse_postorder(visitor & v) const;
+void ex::traverse(visitor & v) const;
+@end example
+
+@code{traverse_preorder()} visits a node @emph{before} visiting its
+subexpressions, while @code{traverse_postorder()} visits a node @emph{after}
+visiting its subexpressions. @code{traverse()} is a synonym for
+@code{traverse_preorder()}.
+
+Here is a new implementation of @code{gather_indices()} that uses the visitor
+and @code{traverse()}:
+
+@example
+lst gather_indices(const ex & e)
+@{
+ gather_indices_visitor v;
+ e.traverse(v);
+ return v.get_result();
+@}
+@end example
+
+Alternatively, you could use pre- or postorder iterators for the tree
+traversal:
+
+@example
+lst gather_indices(const ex & e)
+@{
+ gather_indices_visitor v;
+ for (const_preorder_iterator i = e.preorder_begin();
+ i != e.preorder_end(); ++i) @{
+ i->accept(v);
+ @}
+ return v.get_result();
+@}
+@end example
+
+
+@node Polynomial Arithmetic, Rational Expressions, Visitors and Tree Traversal, Methods and Functions
+@c node-name, next, previous, up
+@section Polynomial arithmetic
+
+@subsection Expanding and collecting
+@cindex @code{expand()}
+@cindex @code{collect()}
+@cindex @code{collect_common_factors()}
+
+A polynomial in one or more variables has many equivalent
+representations. Some useful ones serve a specific purpose. Consider
+for example the trivariate polynomial @math{4*x*y + x*z + 20*y^2 +
+21*y*z + 4*z^2} (written down here in output-style). It is equivalent
+to the factorized polynomial @math{(x + 5*y + 4*z)*(4*y + z)}. Other
+representations are the recursive ones where one collects for exponents
+in one of the three variable. Since the factors are themselves
+polynomials in the remaining two variables the procedure can be
+repeated. In our example, two possibilities would be @math{(4*y + z)*x
++ 20*y^2 + 21*y*z + 4*z^2} and @math{20*y^2 + (21*z + 4*x)*y + 4*z^2 +
+x*z}.
+
+To bring an expression into expanded form, its method
+
+@example
+ex ex::expand(unsigned options = 0);
+@end example
+
+may be called. In our example above, this corresponds to @math{4*x*y +
+x*z + 20*y^2 + 21*y*z + 4*z^2}. Again, since the canonical form in
+GiNaC is not easy to guess you should be prepared to see different
+orderings of terms in such sums!
+
+Another useful representation of multivariate polynomials is as a
+univariate polynomial in one of the variables with the coefficients
+being polynomials in the remaining variables. The method
+@code{collect()} accomplishes this task:
+
+@example
+ex ex::collect(const ex & s, bool distributed = false);
+@end example
+
+The first argument to @code{collect()} can also be a list of objects in which
+case the result is either a recursively collected polynomial, or a polynomial
+in a distributed form with terms like @math{c*x1^e1*...*xn^en}, as specified
+by the @code{distributed} flag.
+
+Note that the original polynomial needs to be in expanded form (for the
+variables concerned) in order for @code{collect()} to be able to find the
+coefficients properly.
+
+The following @command{ginsh} transcript shows an application of @code{collect()}
+together with @code{find()}:
+
+@example
+> a=expand((sin(x)+sin(y))*(1+p+q)*(1+d));
+d*p*sin(x)+p*sin(x)+q*d*sin(x)+q*sin(y)+d*sin(x)+q*d*sin(y)+sin(y)+d*sin(y)+q*sin(x)+d*sin(y)*p+sin(x)+sin(y)*p
+> collect(a,@{p,q@});
+d*sin(x)+(d*sin(x)+sin(y)+d*sin(y)+sin(x))*p+(d*sin(x)+sin(y)+d*sin(y)+sin(x))*q+sin(y)+d*sin(y)+sin(x)
+> collect(a,find(a,sin($1)));
+(1+q+d+q*d+d*p+p)*sin(y)+(1+q+d+q*d+d*p+p)*sin(x)
+> collect(a,@{find(a,sin($1)),p,q@});
+(1+(1+d)*p+d+q*(1+d))*sin(x)+(1+(1+d)*p+d+q*(1+d))*sin(y)
+> collect(a,@{find(a,sin($1)),d@});
+(1+q+d*(1+q+p)+p)*sin(y)+(1+q+d*(1+q+p)+p)*sin(x)
+@end example
+
+Polynomials can often be brought into a more compact form by collecting
+common factors from the terms of sums. This is accomplished by the function
+
+@example
+ex collect_common_factors(const ex & e);
+@end example
+
+This function doesn't perform a full factorization but only looks for
+factors which are already explicitly present:
+
+@example
+> collect_common_factors(a*x+a*y);
+(x+y)*a
+> collect_common_factors(a*x^2+2*a*x*y+a*y^2);
+a*(2*x*y+y^2+x^2)
+> collect_common_factors(a*(b*(a+c)*x+b*((a+c)*x+(a+c)*y)*y));
+(c+a)*a*(x*y+y^2+x)*b
+@end example
+
+@subsection Degree and coefficients
+@cindex @code{degree()}
+@cindex @code{ldegree()}
+@cindex @code{coeff()}
+
+The degree and low degree of a polynomial can be obtained using the two
+methods
+
+@example
+int ex::degree(const ex & s);
+int ex::ldegree(const ex & s);
+@end example
+
+which also work reliably on non-expanded input polynomials (they even work
+on rational functions, returning the asymptotic degree). By definition, the
+degree of zero is zero. To extract a coefficient with a certain power from
+an expanded polynomial you use
+
+@example
+ex ex::coeff(const ex & s, int n);
+@end example
+
+You can also obtain the leading and trailing coefficients with the methods
+
+@example
+ex ex::lcoeff(const ex & s);
+ex ex::tcoeff(const ex & s);
+@end example
+
+which are equivalent to @code{coeff(s, degree(s))} and @code{coeff(s, ldegree(s))},
+respectively.
+
+An application is illustrated in the next example, where a multivariate
+polynomial is analyzed:
+
+@example
+@{
+ symbol x("x"), y("y");
+ ex PolyInp = 4*pow(x,3)*y + 5*x*pow(y,2) + 3*y
+ - pow(x+y,2) + 2*pow(y+2,2) - 8;
+ ex Poly = PolyInp.expand();
+
+ for (int i=Poly.ldegree(x); i<=Poly.degree(x); ++i) @{
+ cout << "The x^" << i << "-coefficient is "
+ << Poly.coeff(x,i) << endl;
+ @}
+ cout << "As polynomial in y: "
+ << Poly.collect(y) << endl;
+@}
+@end example
+
+When run, it returns an output in the following fashion:
+
+@example
+The x^0-coefficient is y^2+11*y
+The x^1-coefficient is 5*y^2-2*y
+The x^2-coefficient is -1
+The x^3-coefficient is 4*y
+As polynomial in y: -x^2+(5*x+1)*y^2+(-2*x+4*x^3+11)*y
+@end example
+
+As always, the exact output may vary between different versions of GiNaC
+or even from run to run since the internal canonical ordering is not
+within the user's sphere of influence.
+
+@code{degree()}, @code{ldegree()}, @code{coeff()}, @code{lcoeff()},
+@code{tcoeff()} and @code{collect()} can also be used to a certain degree
+with non-polynomial expressions as they not only work with symbols but with
+constants, functions and indexed objects as well:
+
+@example
+@{
+ symbol a("a"), b("b"), c("c"), x("x");
+ idx i(symbol("i"), 3);
+
+ ex e = pow(sin(x) - cos(x), 4);
+ cout << e.degree(cos(x)) << endl;
+ // -> 4
+ cout << e.expand().coeff(sin(x), 3) << endl;
+ // -> -4*cos(x)
+
+ e = indexed(a+b, i) * indexed(b+c, i);
+ e = e.expand(expand_options::expand_indexed);
+ cout << e.collect(indexed(b, i)) << endl;
+ // -> a.i*c.i+(a.i+c.i)*b.i+b.i^2
+@}
+@end example
+
+
+@subsection Polynomial division
+@cindex polynomial division
+@cindex quotient
+@cindex remainder
+@cindex pseudo-remainder
+@cindex @code{quo()}
+@cindex @code{rem()}
+@cindex @code{prem()}
+@cindex @code{divide()}
+
+The two functions
+
+@example
+ex quo(const ex & a, const ex & b, const ex & x);
+ex rem(const ex & a, const ex & b, const ex & x);
+@end example
+
+compute the quotient and remainder of univariate polynomials in the variable
+@samp{x}. The results satisfy @math{a = b*quo(a, b, x) + rem(a, b, x)}.
+
+The additional function
+
+@example
+ex prem(const ex & a, const ex & b, const ex & x);
+@end example
+
+computes the pseudo-remainder of @samp{a} and @samp{b} which satisfies
+@math{c*a = b*q + prem(a, b, x)}, where @math{c = b.lcoeff(x) ^ (a.degree(x) - b.degree(x) + 1)}.
+
+Exact division of multivariate polynomials is performed by the function
+
+@example
+bool divide(const ex & a, const ex & b, ex & q);
+@end example
+
+If @samp{b} divides @samp{a} over the rationals, this function returns @code{true}
+and returns the quotient in the variable @code{q}. Otherwise it returns @code{false}
+in which case the value of @code{q} is undefined.
+
+
+@subsection Unit, content and primitive part
+@cindex @code{unit()}
+@cindex @code{content()}
+@cindex @code{primpart()}
+
+The methods
+
+@example
+ex ex::unit(const ex & x);
+ex ex::content(const ex & x);
+ex ex::primpart(const ex & x);
+@end example
+
+return the unit part, content part, and primitive polynomial of a multivariate
+polynomial with respect to the variable @samp{x} (the unit part being the sign
+of the leading coefficient, the content part being the GCD of the coefficients,
+and the primitive polynomial being the input polynomial divided by the unit and
+content parts). The product of unit, content, and primitive part is the
+original polynomial.
+
+
+@subsection GCD, LCM and resultant
+@cindex GCD
+@cindex LCM
+@cindex @code{gcd()}
+@cindex @code{lcm()}
+
+The functions for polynomial greatest common divisor and least common
+multiple have the synopsis
+
+@example
+ex gcd(const ex & a, const ex & b);
+ex lcm(const ex & a, const ex & b);
+@end example
+
+The functions @code{gcd()} and @code{lcm()} accept two expressions
+@code{a} and @code{b} as arguments and return a new expression, their
+greatest common divisor or least common multiple, respectively. If the
+polynomials @code{a} and @code{b} are coprime @code{gcd(a,b)} returns 1
+and @code{lcm(a,b)} returns the product of @code{a} and @code{b}.
+
+@example
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+int main()
+@{
+ symbol x("x"), y("y"), z("z");
+ ex P_a = 4*x*y + x*z + 20*pow(y, 2) + 21*y*z + 4*pow(z, 2);
+ ex P_b = x*y + 3*x*z + 5*pow(y, 2) + 19*y*z + 12*pow(z, 2);
+
+ ex P_gcd = gcd(P_a, P_b);
+ // x + 5*y + 4*z
+ ex P_lcm = lcm(P_a, P_b);
+ // 4*x*y^2 + 13*y*x*z + 20*y^3 + 81*y^2*z + 67*y*z^2 + 3*x*z^2 + 12*z^3
+@}
+@end example
+
+@cindex resultant
+@cindex @code{resultant()}
+
+The resultant of two expressions only makes sense with polynomials.
+It is always computed with respect to a specific symbol within the
+expressions. The function has the interface
+
+@example
+ex resultant(const ex & a, const ex & b, const ex & s);
+@end example
+
+Resultants are symmetric in @code{a} and @code{b}. The following example
+computes the resultant of two expressions with respect to @code{x} and
+@code{y}, respectively:
+
+@example
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+int main()
+@{
+ symbol x("x"), y("y");
+
+ ex e1 = x+pow(y,2), e2 = 2*pow(x,3)-1; // x+y^2, 2*x^3-1
+ ex r;
+
+ r = resultant(e1, e2, x);
+ // -> 1+2*y^6
+ r = resultant(e1, e2, y);
+ // -> 1-4*x^3+4*x^6
+@}
+@end example
+
+@subsection Square-free decomposition
+@cindex square-free decomposition
+@cindex factorization
+@cindex @code{sqrfree()}
+
+GiNaC still lacks proper factorization support. Some form of
+factorization is, however, easily implemented by noting that factors
+appearing in a polynomial with power two or more also appear in the
+derivative and hence can easily be found by computing the GCD of the
+original polynomial and its derivatives. Any decent system has an
+interface for this so called square-free factorization. So we provide
+one, too:
+@example
+ex sqrfree(const ex & a, const lst & l = lst());
+@end example
+Here is an example that by the way illustrates how the exact form of the
+result may slightly depend on the order of differentiation, calling for
+some care with subsequent processing of the result:
+@example
+ ...
+ symbol x("x"), y("y");
+ ex BiVarPol = expand(pow(2-2*y,3) * pow(1+x*y,2) * pow(x-2*y,2) * (x+y));
+
+ cout << sqrfree(BiVarPol, lst(x,y)) << endl;
+ // -> 8*(1-y)^3*(y*x^2-2*y+x*(1-2*y^2))^2*(y+x)
+
+ cout << sqrfree(BiVarPol, lst(y,x)) << endl;
+ // -> 8*(1-y)^3*(-y*x^2+2*y+x*(-1+2*y^2))^2*(y+x)
+
+ cout << sqrfree(BiVarPol) << endl;
+ // -> depending on luck, any of the above
+ ...
+@end example
+Note also, how factors with the same exponents are not fully factorized
+with this method.
+
+
+@node Rational Expressions, Symbolic Differentiation, Polynomial Arithmetic, Methods and Functions
+@c node-name, next, previous, up
+@section Rational expressions
+
+@subsection The @code{normal} method
+@cindex @code{normal()}
+@cindex simplification
+@cindex temporary replacement
+
+Some basic form of simplification of expressions is called for frequently.
+GiNaC provides the method @code{.normal()}, which converts a rational function
+into an equivalent rational function of the form @samp{numerator/denominator}
+where numerator and denominator are coprime. If the input expression is already
+a fraction, it just finds the GCD of numerator and denominator and cancels it,
+otherwise it performs fraction addition and multiplication.
+
+@code{.normal()} can also be used on expressions which are not rational functions
+as it will replace all non-rational objects (like functions or non-integer
+powers) by temporary symbols to bring the expression to the domain of rational
+functions before performing the normalization, and re-substituting these
+symbols afterwards. This algorithm is also available as a separate method
+@code{.to_rational()}, described below.
+
+This means that both expressions @code{t1} and @code{t2} are indeed
+simplified in this little code snippet:
+
+@example
+@{
+ symbol x("x");
+ ex t1 = (pow(x,2) + 2*x + 1)/(x + 1);
+ ex t2 = (pow(sin(x),2) + 2*sin(x) + 1)/(sin(x) + 1);
+ std::cout << "t1 is " << t1.normal() << std::endl;
+ std::cout << "t2 is " << t2.normal() << std::endl;
+@}
+@end example
+
+Of course this works for multivariate polynomials too, so the ratio of
+the sample-polynomials from the section about GCD and LCM above would be
+normalized to @code{P_a/P_b} = @code{(4*y+z)/(y+3*z)}.
+
+
+@subsection Numerator and denominator
+@cindex numerator
+@cindex denominator
+@cindex @code{numer()}
+@cindex @code{denom()}
+@cindex @code{numer_denom()}
+
+The numerator and denominator of an expression can be obtained with
+
+@example
+ex ex::numer();
+ex ex::denom();
+ex ex::numer_denom();
+@end example
+
+These functions will first normalize the expression as described above and
+then return the numerator, denominator, or both as a list, respectively.
+If you need both numerator and denominator, calling @code{numer_denom()} is
+faster than using @code{numer()} and @code{denom()} separately.
+
+
+@subsection Converting to a polynomial or rational expression
+@cindex @code{to_polynomial()}
+@cindex @code{to_rational()}
+
+Some of the methods described so far only work on polynomials or rational
+functions. GiNaC provides a way to extend the domain of these functions to
+general expressions by using the temporary replacement algorithm described
+above. You do this by calling
+
+@example
+ex ex::to_polynomial(exmap & m);
+ex ex::to_polynomial(lst & l);
+@end example
+or
+@example
+ex ex::to_rational(exmap & m);
+ex ex::to_rational(lst & l);
+@end example
+
+on the expression to be converted. The supplied @code{exmap} or @code{lst}
+will be filled with the generated temporary symbols and their replacement
+expressions in a format that can be used directly for the @code{subs()}
+method. It can also already contain a list of replacements from an earlier
+application of @code{.to_polynomial()} or @code{.to_rational()}, so it's
+possible to use it on multiple expressions and get consistent results.
+
+The difference between @code{.to_polynomial()} and @code{.to_rational()}
+is probably best illustrated with an example:
+
+@example
+@{
+ symbol x("x"), y("y");
+ ex a = 2*x/sin(x) - y/(3*sin(x));
+ cout << a << endl;
+
+ lst lp;
+ ex p = a.to_polynomial(lp);
+ cout << " = " << p << "\n with " << lp << endl;
+ // = symbol3*symbol2*y+2*symbol2*x
+ // with @{symbol2==sin(x)^(-1),symbol3==-1/3@}
+
+ lst lr;
+ ex r = a.to_rational(lr);
+ cout << " = " << r << "\n with " << lr << endl;
+ // = -1/3*symbol4^(-1)*y+2*symbol4^(-1)*x
+ // with @{symbol4==sin(x)@}
+@}
+@end example
+
+The following more useful example will print @samp{sin(x)-cos(x)}:
+
+@example
+@{
+ symbol x("x");
+ ex a = pow(sin(x), 2) - pow(cos(x), 2);
+ ex b = sin(x) + cos(x);
+ ex q;
+ exmap m;
+ divide(a.to_polynomial(m), b.to_polynomial(m), q);
+ cout << q.subs(m) << endl;
+@}
+@end example
+
+
+@node Symbolic Differentiation, Series Expansion, Rational Expressions, Methods and Functions
+@c node-name, next, previous, up
+@section Symbolic differentiation
+@cindex differentiation
+@cindex @code{diff()}
+@cindex chain rule
+@cindex product rule
+
+GiNaC's objects know how to differentiate themselves. Thus, a
+polynomial (class @code{add}) knows that its derivative is the sum of
+the derivatives of all the monomials:
+
+@example
+@{
+ symbol x("x"), y("y"), z("z");
+ ex P = pow(x, 5) + pow(x, 2) + y;
+
+ cout << P.diff(x,2) << endl;
+ // -> 20*x^3 + 2
+ cout << P.diff(y) << endl; // 1
+ // -> 1
+ cout << P.diff(z) << endl; // 0
+ // -> 0
+@}
+@end example
+
+If a second integer parameter @var{n} is given, the @code{diff} method
+returns the @var{n}th derivative.
+
+If @emph{every} object and every function is told what its derivative
+is, all derivatives of composed objects can be calculated using the
+chain rule and the product rule. Consider, for instance the expression
+@code{1/cosh(x)}. Since the derivative of @code{cosh(x)} is
+@code{sinh(x)} and the derivative of @code{pow(x,-1)} is
+@code{-pow(x,-2)}, GiNaC can readily compute the composition. It turns
+out that the composition is the generating function for Euler Numbers,
+i.e. the so called @var{n}th Euler number is the coefficient of
+@code{x^n/n!} in the expansion of @code{1/cosh(x)}. We may use this
+identity to code a function that generates Euler numbers in just three
+lines:
+
+@cindex Euler numbers
+@example
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+ex EulerNumber(unsigned n)
+@{
+ symbol x;
+ const ex generator = pow(cosh(x),-1);
+ return generator.diff(x,n).subs(x==0);
+@}
+
+int main()
+@{
+ for (unsigned i=0; i<11; i+=2)
+ std::cout << EulerNumber(i) << std::endl;
+ return 0;
+@}
+@end example
+
+When you run it, it produces the sequence @code{1}, @code{-1}, @code{5},
+@code{-61}, @code{1385}, @code{-50521}. We increment the loop variable
+@code{i} by two since all odd Euler numbers vanish anyways.
+
+
+@node Series Expansion, Symmetrization, Symbolic Differentiation, Methods and Functions
+@c node-name, next, previous, up
+@section Series expansion
+@cindex @code{series()}
+@cindex Taylor expansion
+@cindex Laurent expansion
+@cindex @code{pseries} (class)
+@cindex @code{Order()}
+
+Expressions know how to expand themselves as a Taylor series or (more
+generally) a Laurent series. As in most conventional Computer Algebra
+Systems, no distinction is made between those two. There is a class of
+its own for storing such series (@code{class pseries}) and a built-in
+function (called @code{Order}) for storing the order term of the series.
+As a consequence, if you want to work with series, i.e. multiply two
+series, you need to call the method @code{ex::series} again to convert
+it to a series object with the usual structure (expansion plus order
+term). A sample application from special relativity could read:
+
+@example
+#include <ginac/ginac.h>
+using namespace std;
+using namespace GiNaC;
+
+int main()
+@{
+ symbol v("v"), c("c");
+
+ ex gamma = 1/sqrt(1 - pow(v/c,2));
+ ex mass_nonrel = gamma.series(v==0, 10);
+
+ cout << "the relativistic mass increase with v is " << endl
+ << mass_nonrel << endl;
+
+ cout << "the inverse square of this series is " << endl
+ << pow(mass_nonrel,-2).series(v==0, 10) << endl;
+@}
+@end example
+
+Only calling the series method makes the last output simplify to
+@math{1-v^2/c^2+O(v^10)}, without that call we would just have a long
+series raised to the power @math{-2}.
+
+@cindex Machin's formula
+As another instructive application, let us calculate the numerical
+value of Archimedes' constant
+@tex
+$\pi$
+@end tex
+(for which there already exists the built-in constant @code{Pi})
+using John Machin's amazing formula
+@tex
+$\pi=16$~atan~$\!\left(1 \over 5 \right)-4$~atan~$\!\left(1 \over 239 \right)$.
+@end tex
+@ifnottex
+@math{Pi==16*atan(1/5)-4*atan(1/239)}.
+@end ifnottex
+This equation (and similar ones) were used for over 200 years for
+computing digits of pi (see @cite{Pi Unleashed}). We may expand the
+arcus tangent around @code{0} and insert the fractions @code{1/5} and
+@code{1/239}. However, as we have seen, a series in GiNaC carries an
+order term with it and the question arises what the system is supposed
+to do when the fractions are plugged into that order term. The solution
+is to use the function @code{series_to_poly()} to simply strip the order
+term off:
+
+@example
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+ex machin_pi(int degr)
+@{
+ symbol x;
+ ex pi_expansion = series_to_poly(atan(x).series(x,degr));
+ ex pi_approx = 16*pi_expansion.subs(x==numeric(1,5))
+ -4*pi_expansion.subs(x==numeric(1,239));
+ return pi_approx;
+@}
+
+int main()
+@{
+ using std::cout; // just for fun, another way of...
+ using std::endl; // ...dealing with this namespace std.
+ ex pi_frac;
+ for (int i=2; i<12; i+=2) @{
+ pi_frac = machin_pi(i);
+ cout << i << ":\t" << pi_frac << endl
+ << "\t" << pi_frac.evalf() << endl;
+ @}
+ return 0;
+@}
+@end example
+
+Note how we just called @code{.series(x,degr)} instead of
+@code{.series(x==0,degr)}. This is a simple shortcut for @code{ex}'s
+method @code{series()}: if the first argument is a symbol the expression
+is expanded in that symbol around point @code{0}. When you run this
+program, it will type out:
+
+@example
+2: 3804/1195
+ 3.1832635983263598326
+4: 5359397032/1706489875
+ 3.1405970293260603143
+6: 38279241713339684/12184551018734375
+ 3.141621029325034425
+8: 76528487109180192540976/24359780855939418203125
+ 3.141591772182177295
+10: 327853873402258685803048818236/104359128170408663038552734375
+ 3.1415926824043995174
+@end example
+
+
+@node Symmetrization, Built-in Functions, Series Expansion, Methods and Functions
+@c node-name, next, previous, up
+@section Symmetrization
+@cindex @code{symmetrize()}
+@cindex @code{antisymmetrize()}
+@cindex @code{symmetrize_cyclic()}
+
+The three methods
+
+@example
+ex ex::symmetrize(const lst & l);
+ex ex::antisymmetrize(const lst & l);
+ex ex::symmetrize_cyclic(const lst & l);
+@end example
+
+symmetrize an expression by returning the sum over all symmetric,
+antisymmetric or cyclic permutations of the specified list of objects,
+weighted by the number of permutations.
+
+The three additional methods
+
+@example
+ex ex::symmetrize();
+ex ex::antisymmetrize();
+ex ex::symmetrize_cyclic();
+@end example
+
+symmetrize or antisymmetrize an expression over its free indices.
+
+Symmetrization is most useful with indexed expressions but can be used with
+almost any kind of object (anything that is @code{subs()}able):
+
+@example
+@{
+ idx i(symbol("i"), 3), j(symbol("j"), 3), k(symbol("k"), 3);
+ symbol A("A"), B("B"), a("a"), b("b"), c("c");
+
+ cout << indexed(A, i, j).symmetrize() << endl;
+ // -> 1/2*A.j.i+1/2*A.i.j
+ cout << indexed(A, i, j, k).antisymmetrize(lst(i, j)) << endl;
+ // -> -1/2*A.j.i.k+1/2*A.i.j.k
+ cout << lst(a, b, c).symmetrize_cyclic(lst(a, b, c)) << endl;
+ // -> 1/3*@{a,b,c@}+1/3*@{b,c,a@}+1/3*@{c,a,b@}
+@}
+@end example
+
+@node Built-in Functions, Multiple polylogarithms, Symmetrization, Methods and Functions
+@c node-name, next, previous, up
+@section Predefined mathematical functions
+@c
+@subsection Overview
+
+GiNaC contains the following predefined mathematical functions:
+
+@cartouche
+@multitable @columnfractions .30 .70
+@item @strong{Name} @tab @strong{Function}
+@item @code{abs(x)}
+@tab absolute value
+@cindex @code{abs()}
+@item @code{csgn(x)}
+@tab complex sign
+@cindex @code{conjugate()}
+@item @code{conjugate(x)}
+@tab complex conjugation
+@cindex @code{csgn()}
+@item @code{sqrt(x)}
+@tab square root (not a GiNaC function, rather an alias for @code{pow(x, numeric(1, 2))})
+@cindex @code{sqrt()}
+@item @code{sin(x)}
+@tab sine
+@cindex @code{sin()}
+@item @code{cos(x)}
+@tab cosine
+@cindex @code{cos()}
+@item @code{tan(x)}
+@tab tangent
+@cindex @code{tan()}
+@item @code{asin(x)}
+@tab inverse sine
+@cindex @code{asin()}
+@item @code{acos(x)}
+@tab inverse cosine
+@cindex @code{acos()}
+@item @code{atan(x)}
+@tab inverse tangent
+@cindex @code{atan()}
+@item @code{atan2(y, x)}
+@tab inverse tangent with two arguments
+@item @code{sinh(x)}
+@tab hyperbolic sine
+@cindex @code{sinh()}
+@item @code{cosh(x)}
+@tab hyperbolic cosine
+@cindex @code{cosh()}
+@item @code{tanh(x)}
+@tab hyperbolic tangent
+@cindex @code{tanh()}
+@item @code{asinh(x)}
+@tab inverse hyperbolic sine
+@cindex @code{asinh()}
+@item @code{acosh(x)}
+@tab inverse hyperbolic cosine
+@cindex @code{acosh()}
+@item @code{atanh(x)}
+@tab inverse hyperbolic tangent
+@cindex @code{atanh()}
+@item @code{exp(x)}
+@tab exponential function
+@cindex @code{exp()}
+@item @code{log(x)}
+@tab natural logarithm
+@cindex @code{log()}
+@item @code{Li2(x)}
+@tab dilogarithm
+@cindex @code{Li2()}
+@item @code{Li(m, x)}
+@tab classical polylogarithm as well as multiple polylogarithm
+@cindex @code{Li()}
+@item @code{S(n, p, x)}
+@tab Nielsen's generalized polylogarithm
+@cindex @code{S()}
+@item @code{H(m, x)}
+@tab harmonic polylogarithm
+@cindex @code{H()}
+@item @code{zeta(m)}
+@tab Riemann's zeta function as well as multiple zeta value
+@cindex @code{zeta()}
+@item @code{zeta(m, s)}
+@tab alternating Euler sum
+@cindex @code{zeta()}
+@item @code{zetaderiv(n, x)}
+@tab derivatives of Riemann's zeta function
+@item @code{tgamma(x)}
+@tab gamma function
+@cindex @code{tgamma()}
+@cindex gamma function
+@item @code{lgamma(x)}
+@tab logarithm of gamma function
+@cindex @code{lgamma()}
+@item @code{beta(x, y)}
+@tab beta function (@code{tgamma(x)*tgamma(y)/tgamma(x+y)})
+@cindex @code{beta()}
+@item @code{psi(x)}
+@tab psi (digamma) function
+@cindex @code{psi()}
+@item @code{psi(n, x)}
+@tab derivatives of psi function (polygamma functions)
+@item @code{factorial(n)}
+@tab factorial function @math{n!}
+@cindex @code{factorial()}
+@item @code{binomial(n, k)}
+@tab binomial coefficients
+@cindex @code{binomial()}
+@item @code{Order(x)}
+@tab order term function in truncated power series
+@cindex @code{Order()}
+@end multitable
+@end cartouche
+
+@cindex branch cut
+For functions that have a branch cut in the complex plane GiNaC follows
+the conventions for C++ as defined in the ANSI standard as far as
+possible. In particular: the natural logarithm (@code{log}) and the
+square root (@code{sqrt}) both have their branch cuts running along the
+negative real axis where the points on the axis itself belong to the
+upper part (i.e. continuous with quadrant II). The inverse
+trigonometric and hyperbolic functions are not defined for complex
+arguments by the C++ standard, however. In GiNaC we follow the
+conventions used by CLN, which in turn follow the carefully designed
+definitions in the Common Lisp standard. It should be noted that this
+convention is identical to the one used by the C99 standard and by most
+serious CAS. It is to be expected that future revisions of the C++
+standard incorporate these functions in the complex domain in a manner
+compatible with C99.
+
+@node Multiple polylogarithms, Complex Conjugation, Built-in Functions, Methods and Functions
+@c node-name, next, previous, up
+@subsection Multiple polylogarithms
+
+@cindex polylogarithm
+@cindex Nielsen's generalized polylogarithm
+@cindex harmonic polylogarithm
+@cindex multiple zeta value
+@cindex alternating Euler sum
+@cindex multiple polylogarithm
+
+The multiple polylogarithm is the most generic member of a family of functions,
+to which others like the harmonic polylogarithm, Nielsen's generalized
+polylogarithm and the multiple zeta value belong.
+Everyone of these functions can also be written as a multiple polylogarithm with specific
+parameters. This whole family of functions is therefore often referred to simply as
+multiple polylogarithms, containing @code{Li}, @code{H}, @code{S} and @code{zeta}.
+
+To facilitate the discussion of these functions we distinguish between indices and
+arguments as parameters. In the table above indices are printed as @code{m}, @code{s},
+@code{n} or @code{p}, whereas arguments are printed as @code{x}.
+
+To define a @code{Li}, @code{H} or @code{zeta} with a depth greater than one, you have to
+pass a GiNaC @code{lst} for the indices @code{m} and @code{s}, and in the case of @code{Li}
+for the argument @code{x} as well.
+Note that @code{Li} and @code{zeta} are polymorphic in this respect. They can stand in for
+the classical polylogarithm and Riemann's zeta function (if depth is one), as well as for
+the multiple polylogarithm and the multiple zeta value, respectively. Note also, that
+GiNaC doesn't check whether the @code{lst}s for two parameters do have the same length.
+It is up to the user to ensure this, otherwise evaluating will result in undefined behavior.
+
+The functions print in LaTeX format as
+@tex
+${\rm Li\;\!}_{m_1,m_2,\ldots,m_k}(x_1,x_2,\ldots,x_k)$,
+@end tex
+@tex
+${\rm S}_{n,p}(x)$,
+@end tex
+@tex
+${\rm H\;\!}_{m_1,m_2,\ldots,m_k}(x)$ and
+@end tex
+@tex
+$\zeta(m_1,m_2,\ldots,m_k)$.
+@end tex
+If @code{zeta} is an alternating zeta sum, i.e. @code{zeta(m,s)}, the indices with negative sign
+are printed with a line above, e.g.
+@tex
+$\zeta(5,\overline{2})$.
+@end tex
+The order of indices and arguments in the GiNaC @code{lst}s and in the output is the same.
+
+Definitions and analytical as well as numerical properties of multiple polylogarithms
+are too numerous to be covered here. Instead, the user is referred to the publications listed at the
+end of this section. The implementation in GiNaC adheres to the definitions and conventions therein,
+except for a few differences which will be explicitly stated in the following.
+
+One difference is about the order of the indices and arguments. For GiNaC we adopt the convention
+that the indices and arguments are understood to be in the same order as in which they appear in
+the series representation. This means
+@tex
+${\rm Li\;\!}_{m_1,m_2,m_3}(x,1,1) = {\rm H\;\!}_{m_1,m_2,m_3}(x)$ and
+@end tex
+@tex
+${\rm Li\;\!}_{2,1}(1,1) = \zeta(2,1) = \zeta(3)$, but
+@end tex
+@tex
+$\zeta(1,2)$ evaluates to infinity.
+@end tex
+So in comparison to the referenced publications the order of indices and arguments for @code{Li}
+is reversed.
+
+The functions only evaluate if the indices are integers greater than zero, except for the indices
+@code{s} in @code{zeta} and @code{m} in @code{H}. Since @code{s} will be interpreted as the sequence
+of signs for the corresponding indices @code{m}, it must contain 1 or -1, e.g.
+@code{zeta(lst(3,4), lst(-1,1))} means
+@tex
+$\zeta(\overline{3},4)$.
+@end tex
+The definition of @code{H} allows indices to be 0, 1 or -1 (in expanded notation) or equally to
+be any integer (in compact notation). With GiNaC expanded and compact notation can be mixed,
+e.g. @code{lst(0,0,-1,0,1,0,0)}, @code{lst(0,0,-1,2,0,0)} and @code{lst(-3,2,0,0)} are equivalent as
+indices. The anonymous evaluator @code{eval()} tries to reduce the functions, if possible, to
+the least-generic multiple polylogarithm. If all arguments are unit, it returns @code{zeta}.
+Arguments equal to zero get considered, too. Riemann's zeta function @code{zeta} (with depth one)
+evaluates also for negative integers and positive even integers. For example:
+
+@example
+> Li(@{3,1@},@{x,1@});
+S(2,2,x)
+> H(@{-3,2@},1);
+-zeta(@{3,2@},@{-1,-1@})
+> S(3,1,1);
+1/90*Pi^4
+@end example
+
+It is easy to tell for a given function into which other function it can be rewritten, may
+it be a less-generic or a more-generic one, except for harmonic polylogarithms @code{H}
+with negative indices or trailing zeros (the example above gives a hint). Signs can
+quickly be messed up, for example. Therefore GiNaC offers a C++ function
+@code{convert_H_to_Li()} to deal with the upgrade of a @code{H} to a multiple polylogarithm
+@code{Li} (@code{eval()} already cares for the possible downgrade):
+
+@example
+> convert_H_to_Li(@{0,-2,-1,3@},x);
+Li(@{3,1,3@},@{-x,1,-1@})
+> convert_H_to_Li(@{2,-1,0@},x);
+-Li(@{2,1@},@{x,-1@})*log(x)+2*Li(@{3,1@},@{x,-1@})+Li(@{2,2@},@{x,-1@})
+@end example
+
+Every function apart from the multiple polylogarithm @code{Li} can be numerically evaluated for
+arbitrary real or complex arguments. @code{Li} only evaluates if for all arguments
+@tex
+$x_i$ the condition
+@end tex
+@tex
+$x_1x_2\cdots x_i < 1$ holds.
+@end tex
+
+@example
+> Digits=100;
+100
+> evalf(zeta(@{3,1,3,1@}));
+0.005229569563530960100930652283899231589890420784634635522547448972148869544...
+@end example
+
+Note that the convention for arguments on the branch cut in GiNaC as stated above is
+different from the one Remiddi and Vermaseren have chosen for the harmonic polylogarithm.
+
+If a function evaluates to infinity, no exceptions are raised, but the function is returned
+unevaluated, e.g.
+@tex
+$\zeta(1)$.
+@end tex
+In long expressions this helps a lot with debugging, because you can easily spot
+the divergencies. But on the other hand, you have to make sure for yourself, that no illegal
+cancellations of divergencies happen.
+
+Useful publications:
+
+@cite{Nested Sums, Expansion of Transcendental Functions and Multi-Scale Multi-Loop Integrals},
+S.Moch, P.Uwer, S.Weinzierl, hep-ph/0110083
+
+@cite{Harmonic Polylogarithms},
+E.Remiddi, J.A.M.Vermaseren, Int.J.Mod.Phys. A15 (2000), pp. 725-754
+
+@cite{Special Values of Multiple Polylogarithms},
+J.Borwein, D.Bradley, D.Broadhurst, P.Lisonek, Trans.Amer.Math.Soc. 353/3 (2001), pp. 907-941
+
+@node Complex Conjugation, Solving Linear Systems of Equations, Multiple polylogarithms, Methods and Functions
+@c node-name, next, previous, up
+@section Complex Conjugation
+@c
+@cindex @code{conjugate()}
+
+The method
+
+@example
+ex ex::conjugate();
+@end example
+
+returns the complex conjugate of the expression. For all built-in functions and objects the
+conjugation gives the expected results:
+
+@example
+@{
+ varidx a(symbol("a"), 4), b(symbol("b"), 4);
+ symbol x("x");
+ realsymbol y("y");
+
+ cout << (3*I*x*y + sin(2*Pi*I*y)).conjugate() << endl;
+ // -> -3*I*conjugate(x)*y+sin(-2*I*Pi*y)
+ cout << (dirac_gamma(a)*dirac_gamma(b)*dirac_gamma5()).conjugate() << endl;
+ // -> -gamma5*gamma~b*gamma~a
+@}
+@end example
+
+For symbols in the complex domain the conjugation can not be evaluated and the GiNaC function
+@code{conjugate} is returned. GiNaC functions conjugate by applying the conjugation to their
+arguments. This is the default strategy. If you want to define your own functions and want to
+change this behavior, you have to supply a specialized conjugation method for your function
+(see @ref{Symbolic functions} and the GiNaC source-code for @code{abs} as an example).
+
+@node Solving Linear Systems of Equations, Input/Output, Complex Conjugation, Methods and Functions
+@c node-name, next, previous, up
+@section Solving Linear Systems of Equations
+@cindex @code{lsolve()}
+
+The function @code{lsolve()} provides a convenient wrapper around some
+matrix operations that comes in handy when a system of linear equations
+needs to be solved:
+
+@example
+ex lsolve(const ex &eqns, const ex &symbols, unsigned options=solve_algo::automatic);
+@end example
+
+Here, @code{eqns} is a @code{lst} of equalities (i.e. class
+@code{relational}) while @code{symbols} is a @code{lst} of
+indeterminates. (@xref{The Class Hierarchy}, for an exposition of class
+@code{lst}).
+
+It returns the @code{lst} of solutions as an expression. As an example,
+let us solve the two equations @code{a*x+b*y==3} and @code{x-y==b}:
+
+@example
+@{
+ symbol a("a"), b("b"), x("x"), y("y");
+ lst eqns, vars;
+ eqns = a*x+b*y==3, x-y==b;
+ vars = x, y;
+ cout << lsolve(eqns, vars) << endl;
+ // -> @{x==(3+b^2)/(b+a),y==(3-b*a)/(b+a)@}
+@end example
+
+When the linear equations @code{eqns} are underdetermined, the solution
+will contain one or more tautological entries like @code{x==x},
+depending on the rank of the system. When they are overdetermined, the
+solution will be an empty @code{lst}. Note the third optional parameter
+to @code{lsolve()}: it accepts the same parameters as
+@code{matrix::solve()}. This is because @code{lsolve} is just a wrapper
+around that method.
+
+
+@node Input/Output, Extending GiNaC, Solving Linear Systems of Equations, Methods and Functions
+@c node-name, next, previous, up
+@section Input and output of expressions
+@cindex I/O
+
+@subsection Expression output
+@cindex printing
+@cindex output of expressions
+
+Expressions can simply be written to any stream:
+
+@example
+@{
+ symbol x("x");
+ ex e = 4.5*I+pow(x,2)*3/2;
+ cout << e << endl; // prints '4.5*I+3/2*x^2'
+ // ...
+@end example
+
+The default output format is identical to the @command{ginsh} input syntax and
+to that used by most computer algebra systems, but not directly pastable
+into a GiNaC C++ program (note that in the above example, @code{pow(x,2)}
+is printed as @samp{x^2}).
+
+It is possible to print expressions in a number of different formats with
+a set of stream manipulators;
+
+@example
+std::ostream & dflt(std::ostream & os);
+std::ostream & latex(std::ostream & os);
+std::ostream & tree(std::ostream & os);
+std::ostream & csrc(std::ostream & os);
+std::ostream & csrc_float(std::ostream & os);
+std::ostream & csrc_double(std::ostream & os);
+std::ostream & csrc_cl_N(std::ostream & os);
+std::ostream & index_dimensions(std::ostream & os);
+std::ostream & no_index_dimensions(std::ostream & os);
+@end example
+
+The @code{tree}, @code{latex} and @code{csrc} formats are also available in
+@command{ginsh} via the @code{print()}, @code{print_latex()} and
+@code{print_csrc()} functions, respectively.
+
+@cindex @code{dflt}
+All manipulators affect the stream state permanently. To reset the output
+format to the default, use the @code{dflt} manipulator:
+
+@example
+ // ...
+ cout << latex; // all output to cout will be in LaTeX format from now on
+ cout << e << endl; // prints '4.5 i+\frac@{3@}@{2@} x^@{2@}'
+ cout << sin(x/2) << endl; // prints '\sin(\frac@{1@}@{2@} x)'
+ cout << dflt; // revert to default output format
+ cout << e << endl; // prints '4.5*I+3/2*x^2'
+ // ...
+@end example
+
+If you don't want to affect the format of the stream you're working with,
+you can output to a temporary @code{ostringstream} like this:
+
+@example
+ // ...
+ ostringstream s;
+ s << latex << e; // format of cout remains unchanged
+ cout << s.str() << endl; // prints '4.5 i+\frac@{3@}@{2@} x^@{2@}'
+ // ...
+@end example
+
+@cindex @code{csrc}
+@cindex @code{csrc_float}
+@cindex @code{csrc_double}
+@cindex @code{csrc_cl_N}
+The @code{csrc} (an alias for @code{csrc_double}), @code{csrc_float},
+@code{csrc_double} and @code{csrc_cl_N} manipulators set the output to a
+format that can be directly used in a C or C++ program. The three possible
+formats select the data types used for numbers (@code{csrc_cl_N} uses the
+classes provided by the CLN library):
+
+@example
+ // ...
+ cout << "f = " << csrc_float << e << ";\n";
+ cout << "d = " << csrc_double << e << ";\n";
+ cout << "n = " << csrc_cl_N << e << ";\n";
+ // ...
+@end example
+
+The above example will produce (note the @code{x^2} being converted to
+@code{x*x}):
+
+@example
+f = (3.0/2.0)*(x*x)+std::complex<float>(0.0,4.5000000e+00);
+d = (3.0/2.0)*(x*x)+std::complex<double>(0.0,4.5000000000000000e+00);
+n = cln::cl_RA("3/2")*(x*x)+cln::complex(cln::cl_I("0"),cln::cl_F("4.5_17"));
+@end example
+
+@cindex @code{tree}
+The @code{tree} manipulator allows dumping the internal structure of an
+expression for debugging purposes:
+
+@example
+ // ...
+ cout << tree << e;
+@}
+@end example
+
+produces
+
+@example
+add, hash=0x0, flags=0x3, nops=2
+ power, hash=0x0, flags=0x3, nops=2
+ x (symbol), serial=0, hash=0xc8d5bcdd, flags=0xf
+ 2 (numeric), hash=0x6526b0fa, flags=0xf
+ 3/2 (numeric), hash=0xf9828fbd, flags=0xf
+ -----
+ overall_coeff
+ 4.5L0i (numeric), hash=0xa40a97e0, flags=0xf
+ =====
+@end example
+
+@cindex @code{latex}
+The @code{latex} output format is for LaTeX parsing in mathematical mode.
+It is rather similar to the default format but provides some braces needed
+by LaTeX for delimiting boxes and also converts some common objects to
+conventional LaTeX names. It is possible to give symbols a special name for
+LaTeX output by supplying it as a second argument to the @code{symbol}
+constructor.
+
+For example, the code snippet
+
+@example
+@{
+ symbol x("x", "\\circ");
+ ex e = lgamma(x).series(x==0,3);
+ cout << latex << e << endl;
+@}
+@end example
+
+will print
+
+@example
+ @{(-\ln(\circ))@}+@{(-\gamma_E)@} \circ+@{(\frac@{1@}@{12@} \pi^@{2@})@} \circ^@{2@}+\mathcal@{O@}(\circ^@{3@})
+@end example
+
+@cindex @code{index_dimensions}
+@cindex @code{no_index_dimensions}
+Index dimensions are normally hidden in the output. To make them visible, use
+the @code{index_dimensions} manipulator. The dimensions will be written in
+square brackets behind each index value in the default and LaTeX output
+formats:
+
+@example
+@{
+ symbol x("x"), y("y");
+ varidx mu(symbol("mu"), 4), nu(symbol("nu"), 4);
+ ex e = indexed(x, mu) * indexed(y, nu);
+
+ cout << e << endl;
+ // prints 'x~mu*y~nu'
+ cout << index_dimensions << e << endl;
+ // prints 'x~mu[4]*y~nu[4]'
+ cout << no_index_dimensions << e << endl;
+ // prints 'x~mu*y~nu'
+@}
+@end example
+
+
+@cindex Tree traversal
+If you need any fancy special output format, e.g. for interfacing GiNaC
+with other algebra systems or for producing code for different
+programming languages, you can always traverse the expression tree yourself:
+
+@example
+static void my_print(const ex & e)
+@{
+ if (is_a<function>(e))
+ cout << ex_to<function>(e).get_name();
+ else
+ cout << ex_to<basic>(e).class_name();
+ cout << "(";
+ size_t n = e.nops();
+ if (n)
+ for (size_t i=0; i<n; i++) @{
+ my_print(e.op(i));
+ if (i != n-1)
+ cout << ",";
+ @}
+ else
+ cout << e;
+ cout << ")";
+@}
+
+int main()
+@{
+ my_print(pow(3, x) - 2 * sin(y / Pi)); cout << endl;
+ return 0;
+@}
+@end example
+
+This will produce
+
+@example
+add(power(numeric(3),symbol(x)),mul(sin(mul(power(constant(Pi),numeric(-1)),
+symbol(y))),numeric(-2)))
+@end example
+
+If you need an output format that makes it possible to accurately
+reconstruct an expression by feeding the output to a suitable parser or
+object factory, you should consider storing the expression in an
+@code{archive} object and reading the object properties from there.
+See the section on archiving for more information.
+
+
+@subsection Expression input
+@cindex input of expressions
+
+GiNaC provides no way to directly read an expression from a stream because
+you will usually want the user to be able to enter something like @samp{2*x+sin(y)}
+and have the @samp{x} and @samp{y} correspond to the symbols @code{x} and
+@code{y} you defined in your program and there is no way to specify the
+desired symbols to the @code{>>} stream input operator.
+
+Instead, GiNaC lets you construct an expression from a string, specifying the
+list of symbols to be used:
+
+@example
+@{
+ symbol x("x"), y("y");
+ ex e("2*x+sin(y)", lst(x, y));
+@}
+@end example
+
+The input syntax is the same as that used by @command{ginsh} and the stream
+output operator @code{<<}. The symbols in the string are matched by name to
+the symbols in the list and if GiNaC encounters a symbol not specified in
+the list it will throw an exception.
+
+With this constructor, it's also easy to implement interactive GiNaC programs:
+
+@example
+#include <iostream>
+#include <string>
+#include <stdexcept>
+#include <ginac/ginac.h>
+using namespace std;
+using namespace GiNaC;
+
+int main()
+@{
+ symbol x("x");
+ string s;
+
+ cout << "Enter an expression containing 'x': ";
+ getline(cin, s);
+
+ try @{
+ ex e(s, lst(x));
+ cout << "The derivative of " << e << " with respect to x is ";
+ cout << e.diff(x) << ".\n";
+ @} catch (exception &p) @{
+ cerr << p.what() << endl;
+ @}
+@}
+@end example
+
+
+@subsection Archiving
+@cindex @code{archive} (class)
+@cindex archiving
+
+GiNaC allows creating @dfn{archives} of expressions which can be stored
+to or retrieved from files. To create an archive, you declare an object
+of class @code{archive} and archive expressions in it, giving each
+expression a unique name:
+
+@example
+#include <fstream>
+using namespace std;
+#include <ginac/ginac.h>
+using namespace GiNaC;
+
+int main()
+@{
+ symbol x("x"), y("y"), z("z");
+
+ ex foo = sin(x + 2*y) + 3*z + 41;
+ ex bar = foo + 1;
+
+ archive a;
+ a.archive_ex(foo, "foo");
+ a.archive_ex(bar, "the second one");
+ // ...
+@end example
+
+The archive can then be written to a file:
+
+@example
+ // ...
+ ofstream out("foobar.gar");
+ out << a;
+ out.close();
+ // ...
+@end example
+
+The file @file{foobar.gar} contains all information that is needed to
+reconstruct the expressions @code{foo} and @code{bar}.
+
+@cindex @command{viewgar}
+The tool @command{viewgar} that comes with GiNaC can be used to view
+the contents of GiNaC archive files:
+
+@example
+$ viewgar foobar.gar
+foo = 41+sin(x+2*y)+3*z
+the second one = 42+sin(x+2*y)+3*z
+@end example
+
+The point of writing archive files is of course that they can later be
+read in again:
+
+@example
+ // ...
+ archive a2;
+ ifstream in("foobar.gar");
+ in >> a2;
+ // ...
+@end example
+
+And the stored expressions can be retrieved by their name:
+
+@example
+ // ...
+ lst syms;
+ syms = x, y;
+
+ ex ex1 = a2.unarchive_ex(syms, "foo");
+ ex ex2 = a2.unarchive_ex(syms, "the second one");
+
+ cout << ex1 << endl; // prints "41+sin(x+2*y)+3*z"
+ cout << ex2 << endl; // prints "42+sin(x+2*y)+3*z"
+ cout << ex1.subs(x == 2) << endl; // prints "41+sin(2+2*y)+3*z"
+@}
+@end example
+
+Note that you have to supply a list of the symbols which are to be inserted
+in the expressions. Symbols in archives are stored by their name only and
+if you don't specify which symbols you have, unarchiving the expression will
+create new symbols with that name. E.g. if you hadn't included @code{x} in
+the @code{syms} list above, the @code{ex1.subs(x == 2)} statement would
+have had no effect because the @code{x} in @code{ex1} would have been a
+different symbol than the @code{x} which was defined at the beginning of
+the program, although both would appear as @samp{x} when printed.
+
+You can also use the information stored in an @code{archive} object to
+output expressions in a format suitable for exact reconstruction. The
+@code{archive} and @code{archive_node} classes have a couple of member
+functions that let you access the stored properties:
+
+@example
+static void my_print2(const archive_node & n)
+@{
+ string class_name;
+ n.find_string("class", class_name);
+ cout << class_name << "(";
+
+ archive_node::propinfovector p;
+ n.get_properties(p);
+
+ size_t num = p.size();
+ for (size_t i=0; i<num; i++) @{
+ const string &name = p[i].name;
+ if (name == "class")
+ continue;
+ cout << name << "=";
+
+ unsigned count = p[i].count;
+ if (count > 1)
+ cout << "@{";
+
+ for (unsigned j=0; j<count; j++) @{
+ switch (p[i].type) @{
+ case archive_node::PTYPE_BOOL: @{
+ bool x;
+ n.find_bool(name, x, j);
+ cout << (x ? "true" : "false");
+ break;
+ @}
+ case archive_node::PTYPE_UNSIGNED: @{
+ unsigned x;
+ n.find_unsigned(name, x, j);
+ cout << x;
+ break;
+ @}
+ case archive_node::PTYPE_STRING: @{
+ string x;
+ n.find_string(name, x, j);
+ cout << '\"' << x << '\"';
+ break;
+ @}
+ case archive_node::PTYPE_NODE: @{
+ const archive_node &x = n.find_ex_node(name, j);
+ my_print2(x);
+ break;
+ @}
+ @}
+
+ if (j != count-1)
+ cout << ",";
+ @}
+
+ if (count > 1)
+ cout << "@}";
+
+ if (i != num-1)
+ cout << ",";
+ @}
+
+ cout << ")";
+@}
+
+int main()
+@{
+ ex e = pow(2, x) - y;
+ archive ar(e, "e");
+ my_print2(ar.get_top_node(0)); cout << endl;
+ return 0;
+@}
+@end example
+
+This will produce:
+
+@example
+add(rest=@{power(basis=numeric(number="2"),exponent=symbol(name="x")),
+symbol(name="y")@},coeff=@{numeric(number="1"),numeric(number="-1")@},
+overall_coeff=numeric(number="0"))
+@end example
+
+Be warned, however, that the set of properties and their meaning for each
+class may change between GiNaC versions.
+
+
+@node Extending GiNaC, What does not belong into GiNaC, Input/Output, Top
+@c node-name, next, previous, up
+@chapter Extending GiNaC
+
+By reading so far you should have gotten a fairly good understanding of
+GiNaC's design patterns. From here on you should start reading the
+sources. All we can do now is issue some recommendations how to tackle
+GiNaC's many loose ends in order to fulfill everybody's dreams. If you
+develop some useful extension please don't hesitate to contact the GiNaC
+authors---they will happily incorporate them into future versions.
+
+@menu
+* What does not belong into GiNaC:: What to avoid.
+* Symbolic functions:: Implementing symbolic functions.
+* Printing:: Adding new output formats.
+* Structures:: Defining new algebraic classes (the easy way).
+* Adding classes:: Defining new algebraic classes (the hard way).
+@end menu
+
+
+@node What does not belong into GiNaC, Symbolic functions, Extending GiNaC, Extending GiNaC
+@c node-name, next, previous, up
+@section What doesn't belong into GiNaC
+
+@cindex @command{ginsh}
+First of all, GiNaC's name must be read literally. It is designed to be
+a library for use within C++. The tiny @command{ginsh} accompanying
+GiNaC makes this even more clear: it doesn't even attempt to provide a
+language. There are no loops or conditional expressions in
+@command{ginsh}, it is merely a window into the library for the
+programmer to test stuff (or to show off). Still, the design of a
+complete CAS with a language of its own, graphical capabilities and all
+this on top of GiNaC is possible and is without doubt a nice project for
+the future.
+
+There are many built-in functions in GiNaC that do not know how to
+evaluate themselves numerically to a precision declared at runtime
+(using @code{Digits}). Some may be evaluated at certain points, but not
+generally. This ought to be fixed. However, doing numerical
+computations with GiNaC's quite abstract classes is doomed to be
+inefficient. For this purpose, the underlying foundation classes
+provided by CLN are much better suited.
+
+
+@node Symbolic functions, Printing, What does not belong into GiNaC, Extending GiNaC
+@c node-name, next, previous, up
+@section Symbolic functions
+
+The easiest and most instructive way to start extending GiNaC is probably to
+create your own symbolic functions. These are implemented with the help of
+two preprocessor macros:
+
+@cindex @code{DECLARE_FUNCTION}
+@cindex @code{REGISTER_FUNCTION}
+@example
+DECLARE_FUNCTION_<n>P(<name>)
+REGISTER_FUNCTION(<name>, <options>)
+@end example
+
+The @code{DECLARE_FUNCTION} macro will usually appear in a header file. It
+declares a C++ function with the given @samp{name} that takes exactly @samp{n}
+parameters of type @code{ex} and returns a newly constructed GiNaC
+@code{function} object that represents your function.
+
+The @code{REGISTER_FUNCTION} macro implements the function. It must be passed
+the same @samp{name} as the respective @code{DECLARE_FUNCTION} macro, and a
+set of options that associate the symbolic function with C++ functions you
+provide to implement the various methods such as evaluation, derivative,
+series expansion etc. They also describe additional attributes the function
+might have, such as symmetry and commutation properties, and a name for
+LaTeX output. Multiple options are separated by the member access operator
+@samp{.} and can be given in an arbitrary order.
+
+(By the way: in case you are worrying about all the macros above we can
+assure you that functions are GiNaC's most macro-intense classes. We have
+done our best to avoid macros where we can.)
+
+@subsection A minimal example
+
+Here is an example for the implementation of a function with two arguments
+that is not further evaluated:
+
+@example
+DECLARE_FUNCTION_2P(myfcn)
+
+REGISTER_FUNCTION(myfcn, dummy())
+@end example
+
+Any code that has seen the @code{DECLARE_FUNCTION} line can use @code{myfcn()}
+in algebraic expressions:
+
+@example
+@{
+ ...
+ symbol x("x");
+ ex e = 2*myfcn(42, 1+3*x) - x;
+ cout << e << endl;
+ // prints '2*myfcn(42,1+3*x)-x'
+ ...
+@}
+@end example
+
+The @code{dummy()} option in the @code{REGISTER_FUNCTION} line signifies
+"no options". A function with no options specified merely acts as a kind of
+container for its arguments. It is a pure "dummy" function with no associated
+logic (which is, however, sometimes perfectly sufficient).
+
+Let's now have a look at the implementation of GiNaC's cosine function for an
+example of how to make an "intelligent" function.
+
+@subsection The cosine function
+
+The GiNaC header file @file{inifcns.h} contains the line
+
+@example
+DECLARE_FUNCTION_1P(cos)
+@end example
+
+which declares to all programs using GiNaC that there is a function @samp{cos}
+that takes one @code{ex} as an argument. This is all they need to know to use
+this function in expressions.
+
+The implementation of the cosine function is in @file{inifcns_trans.cpp}. Here
+is its @code{REGISTER_FUNCTION} line:
+
+@example
+REGISTER_FUNCTION(cos, eval_func(cos_eval).
+ evalf_func(cos_evalf).
+ derivative_func(cos_deriv).
+ latex_name("\\cos"));
+@end example
+
+There are four options defined for the cosine function. One of them
+(@code{latex_name}) gives the function a proper name for LaTeX output; the
+other three indicate the C++ functions in which the "brains" of the cosine
+function are defined.
+
+@cindex @code{hold()}
+@cindex evaluation
+The @code{eval_func()} option specifies the C++ function that implements
+the @code{eval()} method, GiNaC's anonymous evaluator. This function takes
+the same number of arguments as the associated symbolic function (one in this
+case) and returns the (possibly transformed or in some way simplified)
+symbolically evaluated function (@xref{Automatic evaluation}, for a description
+of the automatic evaluation process). If no (further) evaluation is to take
+place, the @code{eval_func()} function must return the original function
+with @code{.hold()}, to avoid a potential infinite recursion. If your
+symbolic functions produce a segmentation fault or stack overflow when
+using them in expressions, you are probably missing a @code{.hold()}
+somewhere.
+
+The @code{eval_func()} function for the cosine looks something like this
+(actually, it doesn't look like this at all, but it should give you an idea
+what is going on):
+
+@example
+static ex cos_eval(const ex & x)
+@{
+ if ("x is a multiple of 2*Pi")
+ return 1;
+ else if ("x is a multiple of Pi")
+ return -1;
+ else if ("x is a multiple of Pi/2")
+ return 0;
+ // more rules...
+
+ else if ("x has the form 'acos(y)'")
+ return y;
+ else if ("x has the form 'asin(y)'")
+ return sqrt(1-y^2);
+ // more rules...
+
+ else
+ return cos(x).hold();
+@}
+@end example
+
+This function is called every time the cosine is used in a symbolic expression:
+
+@example
+@{
+ ...
+ e = cos(Pi);
+ // this calls cos_eval(Pi), and inserts its return value into
+ // the actual expression
+ cout << e << endl;
+ // prints '-1'
+ ...
+@}
+@end example
+
+In this way, @code{cos(4*Pi)} automatically becomes @math{1},
+@code{cos(asin(a+b))} becomes @code{sqrt(1-(a+b)^2)}, etc. If no reasonable
+symbolic transformation can be done, the unmodified function is returned
+with @code{.hold()}.
+
+GiNaC doesn't automatically transform @code{cos(2)} to @samp{-0.416146...}.
+The user has to call @code{evalf()} for that. This is implemented in a
+different function:
+
+@example
+static ex cos_evalf(const ex & x)
+@{
+ if (is_a<numeric>(x))
+ return cos(ex_to<numeric>(x));
+ else
+ return cos(x).hold();
+@}
+@end example
+
+Since we are lazy we defer the problem of numeric evaluation to somebody else,
+in this case the @code{cos()} function for @code{numeric} objects, which in
+turn hands it over to the @code{cos()} function in CLN. The @code{.hold()}
+isn't really needed here, but reminds us that the corresponding @code{eval()}
+function would require it in this place.
+
+Differentiation will surely turn up and so we need to tell @code{cos}
+what its first derivative is (higher derivatives, @code{.diff(x,3)} for
+instance, are then handled automatically by @code{basic::diff} and
+@code{ex::diff}):
+
+@example
+static ex cos_deriv(const ex & x, unsigned diff_param)
+@{
+ return -sin(x);
+@}
+@end example
+
+@cindex product rule
+The second parameter is obligatory but uninteresting at this point. It
+specifies which parameter to differentiate in a partial derivative in
+case the function has more than one parameter, and its main application
+is for correct handling of the chain rule.
+
+An implementation of the series expansion is not needed for @code{cos()} as
+it doesn't have any poles and GiNaC can do Taylor expansion by itself (as
+long as it knows what the derivative of @code{cos()} is). @code{tan()}, on
+the other hand, does have poles and may need to do Laurent expansion:
+
+@example
+static ex tan_series(const ex & x, const relational & rel,
+ int order, unsigned options)
+@{
+ // Find the actual expansion point
+ const ex x_pt = x.subs(rel);
+
+ if ("x_pt is not an odd multiple of Pi/2")
+ throw do_taylor(); // tell function::series() to do Taylor expansion
+
+ // On a pole, expand sin()/cos()
+ return (sin(x)/cos(x)).series(rel, order+2, options);
+@}
+@end example
+
+The @code{series()} implementation of a function @emph{must} return a
+@code{pseries} object, otherwise your code will crash.
+
+@subsection Function options
+
+GiNaC functions understand several more options which are always
+specified as @code{.option(params)}. None of them are required, but you
+need to specify at least one option to @code{REGISTER_FUNCTION()}. There
+is a do-nothing option called @code{dummy()} which you can use to define
+functions without any special options.
+
+@example
+eval_func(<C++ function>)
+evalf_func(<C++ function>)
+derivative_func(<C++ function>)
+series_func(<C++ function>)
+conjugate_func(<C++ function>)
+@end example
+
+These specify the C++ functions that implement symbolic evaluation,
+numeric evaluation, partial derivatives, and series expansion, respectively.
+They correspond to the GiNaC methods @code{eval()}, @code{evalf()},
+@code{diff()} and @code{series()}.
+
+The @code{eval_func()} function needs to use @code{.hold()} if no further
+automatic evaluation is desired or possible.
+
+If no @code{series_func()} is given, GiNaC defaults to simple Taylor
+expansion, which is correct if there are no poles involved. If the function
+has poles in the complex plane, the @code{series_func()} needs to check
+whether the expansion point is on a pole and fall back to Taylor expansion
+if it isn't. Otherwise, the pole usually needs to be regularized by some
+suitable transformation.
+
+@example
+latex_name(const string & n)
+@end example
+
+specifies the LaTeX code that represents the name of the function in LaTeX
+output. The default is to put the function name in an @code{\mbox@{@}}.
+
+@example
+do_not_evalf_params()
+@end example
+
+This tells @code{evalf()} to not recursively evaluate the parameters of the
+function before calling the @code{evalf_func()}.
+
+@example
+set_return_type(unsigned return_type, unsigned return_type_tinfo)
+@end example
+
+This allows you to explicitly specify the commutation properties of the
+function (@xref{Non-commutative objects}, for an explanation of
+(non)commutativity in GiNaC). For example, you can use
+@code{set_return_type(return_types::noncommutative, TINFO_matrix)} to make
+GiNaC treat your function like a matrix. By default, functions inherit the
+commutation properties of their first argument.
+
+@example
+set_symmetry(const symmetry & s)
+@end example
+
+specifies the symmetry properties of the function with respect to its
+arguments. @xref{Indexed objects}, for an explanation of symmetry
+specifications. GiNaC will automatically rearrange the arguments of
+symmetric functions into a canonical order.
+
+Sometimes you may want to have finer control over how functions are
+displayed in the output. For example, the @code{abs()} function prints
+itself as @samp{abs(x)} in the default output format, but as @samp{|x|}
+in LaTeX mode, and @code{fabs(x)} in C source output. This is achieved
+with the
+
+@example
+print_func<C>(<C++ function>)
+@end example
+
+option which is explained in the next section.
+
+@subsection Functions with a variable number of arguments
+
+The @code{DECLARE_FUNCTION} and @code{REGISTER_FUNCTION} macros define
+functions with a fixed number of arguments. Sometimes, though, you may need
+to have a function that accepts a variable number of expressions. One way to
+accomplish this is to pass variable-length lists as arguments. The
+@code{Li()} function uses this method for multiple polylogarithms.
+
+It is also possible to define functions that accept a different number of
+parameters under the same function name, such as the @code{psi()} function
+which can be called either as @code{psi(z)} (the digamma function) or as
+@code{psi(n, z)} (polygamma functions). These are actually two different
+functions in GiNaC that, however, have the same name. Defining such
+functions is not possible with the macros but requires manually fiddling
+with GiNaC internals. If you are interested, please consult the GiNaC source
+code for the @code{psi()} function (@file{inifcns.h} and
+@file{inifcns_gamma.cpp}).
+
+
+@node Printing, Structures, Symbolic functions, Extending GiNaC
+@c node-name, next, previous, up
+@section GiNaC's expression output system
+
+GiNaC allows the output of expressions in a variety of different formats
+(@pxref{Input/Output}). This section will explain how expression output
+is implemented internally, and how to define your own output formats or
+change the output format of built-in algebraic objects. You will also want
+to read this section if you plan to write your own algebraic classes or
+functions.
+
+@cindex @code{print_context} (class)
+@cindex @code{print_dflt} (class)
+@cindex @code{print_latex} (class)
+@cindex @code{print_tree} (class)
+@cindex @code{print_csrc} (class)
+All the different output formats are represented by a hierarchy of classes
+rooted in the @code{print_context} class, defined in the @file{print.h}
+header file:
+
+@table @code
+@item print_dflt
+the default output format
+@item print_latex
+output in LaTeX mathematical mode
+@item print_tree
+a dump of the internal expression structure (for debugging)
+@item print_csrc
+the base class for C source output
+@item print_csrc_float
+C source output using the @code{float} type
+@item print_csrc_double
+C source output using the @code{double} type
+@item print_csrc_cl_N
+C source output using CLN types
+@end table
+
+The @code{print_context} base class provides two public data members:
+
+@example
+class print_context
+@{
+ ...
+public:
+ std::ostream & s;
+ unsigned options;
+@};
+@end example
+
+@code{s} is a reference to the stream to output to, while @code{options}
+holds flags and modifiers. Currently, there is only one flag defined:
+@code{print_options::print_index_dimensions} instructs the @code{idx} class
+to print the index dimension which is normally hidden.
+
+When you write something like @code{std::cout << e}, where @code{e} is
+an object of class @code{ex}, GiNaC will construct an appropriate
+@code{print_context} object (of a class depending on the selected output
+format), fill in the @code{s} and @code{options} members, and call
+
+@cindex @code{print()}
+@example
+void ex::print(const print_context & c, unsigned level = 0) const;
+@end example
+
+which in turn forwards the call to the @code{print()} method of the
+top-level algebraic object contained in the expression.
+
+Unlike other methods, GiNaC classes don't usually override their
+@code{print()} method to implement expression output. Instead, the default
+implementation @code{basic::print(c, level)} performs a run-time double
+dispatch to a function selected by the dynamic type of the object and the
+passed @code{print_context}. To this end, GiNaC maintains a separate method
+table for each class, similar to the virtual function table used for ordinary
+(single) virtual function dispatch.
+
+The method table contains one slot for each possible @code{print_context}
+type, indexed by the (internally assigned) serial number of the type. Slots
+may be empty, in which case GiNaC will retry the method lookup with the
+@code{print_context} object's parent class, possibly repeating the process
+until it reaches the @code{print_context} base class. If there's still no
+method defined, the method table of the algebraic object's parent class
+is consulted, and so on, until a matching method is found (eventually it
+will reach the combination @code{basic/print_context}, which prints the
+object's class name enclosed in square brackets).
+
+You can think of the print methods of all the different classes and output
+formats as being arranged in a two-dimensional matrix with one axis listing
+the algebraic classes and the other axis listing the @code{print_context}
+classes.
+
+Subclasses of @code{basic} can, of course, also overload @code{basic::print()}
+to implement printing, but then they won't get any of the benefits of the
+double dispatch mechanism (such as the ability for derived classes to
+inherit only certain print methods from its parent, or the replacement of
+methods at run-time).
+
+@subsection Print methods for classes
+
+The method table for a class is set up either in the definition of the class,
+by passing the appropriate @code{print_func<C>()} option to
+@code{GINAC_IMPLEMENT_REGISTERED_CLASS_OPT()} (@xref{Adding classes}, for
+an example), or at run-time using @code{set_print_func<T, C>()}. The latter
+can also be used to override existing methods dynamically.
+
+The argument to @code{print_func<C>()} and @code{set_print_func<T, C>()} can
+be a member function of the class (or one of its parent classes), a static
+member function, or an ordinary (global) C++ function. The @code{C} template
+parameter specifies the appropriate @code{print_context} type for which the
+method should be invoked, while, in the case of @code{set_print_func<>()}, the
+@code{T} parameter specifies the algebraic class (for @code{print_func<>()},
+the class is the one being implemented by
+@code{GINAC_IMPLEMENT_REGISTERED_CLASS_OPT}).
+
+For print methods that are member functions, their first argument must be of
+a type convertible to a @code{const C &}, and the second argument must be an
+@code{unsigned}.
+
+For static members and global functions, the first argument must be of a type
+convertible to a @code{const T &}, the second argument must be of a type
+convertible to a @code{const C &}, and the third argument must be an
+@code{unsigned}. A global function will, of course, not have access to
+private and protected members of @code{T}.
+
+The @code{unsigned} argument of the print methods (and of @code{ex::print()}
+and @code{basic::print()}) is used for proper parenthesizing of the output
+(and by @code{print_tree} for proper indentation). It can be used for similar
+purposes if you write your own output formats.
+
+The explanations given above may seem complicated, but in practice it's
+really simple, as shown in the following example. Suppose that we want to
+display exponents in LaTeX output not as superscripts but with little
+upwards-pointing arrows. This can be achieved in the following way:
+
+@example
+void my_print_power_as_latex(const power & p,
+ const print_latex & c,
+ unsigned level)
+@{
+ // get the precedence of the 'power' class
+ unsigned power_prec = p.precedence();
+
+ // if the parent operator has the same or a higher precedence
+ // we need parentheses around the power
+ if (level >= power_prec)
+ c.s << '(';
+
+ // print the basis and exponent, each enclosed in braces, and
+ // separated by an uparrow
+ c.s << '@{';
+ p.op(0).print(c, power_prec);
+ c.s << "@}\\uparrow@{";
+ p.op(1).print(c, power_prec);
+ c.s << '@}';
+
+ // don't forget the closing parenthesis
+ if (level >= power_prec)
+ c.s << ')';
+@}
+
+int main()
+@{
+ // a sample expression
+ symbol x("x"), y("y");
+ ex e = -3*pow(x, 3)*pow(y, -2) + pow(x+y, 2) - 1;
+
+ // switch to LaTeX mode
+ cout << latex;
+
+ // this prints "-1+@{(y+x)@}^@{2@}-3 \frac@{x^@{3@}@}@{y^@{2@}@}"
+ cout << e << endl;
+
+ // now we replace the method for the LaTeX output of powers with
+ // our own one
+ set_print_func<power, print_latex>(my_print_power_as_latex);
+
+ // this prints "-1+@{@{(y+x)@}@}\uparrow@{2@}-3 \frac@{@{x@}\uparrow@{3@}@}@{@{y@}\uparrow@{2@}@}"
+ cout << e << endl;
@}
@end example
-will print @samp{sin(x)-cos(x)}.
+Some notes:
+@itemize
-@node Symbolic Differentiation, Series Expansion, Rational Expressions, Methods and Functions
-@c node-name, next, previous, up
-@section Symbolic differentiation
-@cindex differentiation
-@cindex @code{diff()}
-@cindex chain rule
-@cindex product rule
+@item
+The first argument of @code{my_print_power_as_latex} could also have been
+a @code{const basic &}, the second one a @code{const print_context &}.
-GiNaC's objects know how to differentiate themselves. Thus, a
-polynomial (class @code{add}) knows that its derivative is the sum of
-the derivatives of all the monomials:
+@item
+The above code depends on @code{mul} objects converting their operands to
+@code{power} objects for the purpose of printing.
-@example
-#include <ginac/ginac.h>
-using namespace GiNaC;
+@item
+The output of products including negative powers as fractions is also
+controlled by the @code{mul} class.
-int main()
-@{
- symbol x("x"), y("y"), z("z");
- ex P = pow(x, 5) + pow(x, 2) + y;
+@item
+The @code{power/print_latex} method provided by GiNaC prints square roots
+using @code{\sqrt}, but the above code doesn't.
- cout << P.diff(x,2) << endl; // 20*x^3 + 2
- cout << P.diff(y) << endl; // 1
- cout << P.diff(z) << endl; // 0
-@}
-@end example
+@end itemize
-If a second integer parameter @var{n} is given, the @code{diff} method
-returns the @var{n}th derivative.
+It's not possible to restore a method table entry to its previous or default
+value. Once you have called @code{set_print_func()}, you can only override
+it with another call to @code{set_print_func()}, but you can't easily go back
+to the default behavior again (you can, of course, dig around in the GiNaC
+sources, find the method that is installed at startup
+(@code{power::do_print_latex} in this case), and @code{set_print_func} that
+one; that is, after you circumvent the C++ member access control@dots{}).
-If @emph{every} object and every function is told what its derivative
-is, all derivatives of composed objects can be calculated using the
-chain rule and the product rule. Consider, for instance the expression
-@code{1/cosh(x)}. Since the derivative of @code{cosh(x)} is
-@code{sinh(x)} and the derivative of @code{pow(x,-1)} is
-@code{-pow(x,-2)}, GiNaC can readily compute the composition. It turns
-out that the composition is the generating function for Euler Numbers,
-i.e. the so called @var{n}th Euler number is the coefficient of
-@code{x^n/n!} in the expansion of @code{1/cosh(x)}. We may use this
-identity to code a function that generates Euler numbers in just three
-lines:
+@subsection Print methods for functions
-@cindex Euler numbers
-@example
-#include <ginac/ginac.h>
-using namespace GiNaC;
+Symbolic functions employ a print method dispatch mechanism similar to the
+one used for classes. The methods are specified with @code{print_func<C>()}
+function options. If you don't specify any special print methods, the function
+will be printed with its name (or LaTeX name, if supplied), followed by a
+comma-separated list of arguments enclosed in parentheses.
-ex EulerNumber(unsigned n)
+For example, this is what GiNaC's @samp{abs()} function is defined like:
+
+@example
+static ex abs_eval(const ex & arg) @{ ... @}
+static ex abs_evalf(const ex & arg) @{ ... @}
+
+static void abs_print_latex(const ex & arg, const print_context & c)
@{
- symbol x;
- const ex generator = pow(cosh(x),-1);
- return generator.diff(x,n).subs(x==0);
+ c.s << "@{|"; arg.print(c); c.s << "|@}";
@}
-
-int main()
+
+static void abs_print_csrc_float(const ex & arg, const print_context & c)
@{
- for (unsigned i=0; i<11; i+=2)
- std::cout << EulerNumber(i) << std::endl;
- return 0;
+ c.s << "fabs("; arg.print(c); c.s << ")";
@}
+
+REGISTER_FUNCTION(abs, eval_func(abs_eval).
+ evalf_func(abs_evalf).
+ print_func<print_latex>(abs_print_latex).
+ print_func<print_csrc_float>(abs_print_csrc_float).
+ print_func<print_csrc_double>(abs_print_csrc_float));
@end example
-When you run it, it produces the sequence @code{1}, @code{-1}, @code{5},
-@code{-61}, @code{1385}, @code{-50521}. We increment the loop variable
-@code{i} by two since all odd Euler numbers vanish anyways.
+This will display @samp{abs(x)} as @samp{|x|} in LaTeX mode and @code{fabs(x)}
+in non-CLN C source output, but as @code{abs(x)} in all other formats.
+There is currently no equivalent of @code{set_print_func()} for functions.
-@node Series Expansion, Built-in Functions, Symbolic Differentiation, Methods and Functions
-@c node-name, next, previous, up
-@section Series expansion
-@cindex @code{series()}
-@cindex Taylor expansion
-@cindex Laurent expansion
-@cindex @code{pseries} (class)
+@subsection Adding new output formats
-Expressions know how to expand themselves as a Taylor series or (more
-generally) a Laurent series. As in most conventional Computer Algebra
-Systems, no distinction is made between those two. There is a class of
-its own for storing such series (@code{class pseries}) and a built-in
-function (called @code{Order}) for storing the order term of the series.
-As a consequence, if you want to work with series, i.e. multiply two
-series, you need to call the method @code{ex::series} again to convert
-it to a series object with the usual structure (expansion plus order
-term). A sample application from special relativity could read:
+Creating a new output format involves subclassing @code{print_context},
+which is somewhat similar to adding a new algebraic class
+(@pxref{Adding classes}). There is a macro @code{GINAC_DECLARE_PRINT_CONTEXT}
+that needs to go into the class definition, and a corresponding macro
+@code{GINAC_IMPLEMENT_PRINT_CONTEXT} that has to appear at global scope.
+Every @code{print_context} class needs to provide a default constructor
+and a constructor from an @code{std::ostream} and an @code{unsigned}
+options value.
+
+Here is an example for a user-defined @code{print_context} class:
@example
-#include <ginac/ginac.h>
-using namespace std;
-using namespace GiNaC;
+class print_myformat : public print_dflt
+@{
+ GINAC_DECLARE_PRINT_CONTEXT(print_myformat, print_dflt)
+public:
+ print_myformat(std::ostream & os, unsigned opt = 0)
+ : print_dflt(os, opt) @{@}
+@};
-int main()
+print_myformat::print_myformat() : print_dflt(std::cout) @{@}
+
+GINAC_IMPLEMENT_PRINT_CONTEXT(print_myformat, print_dflt)
+@end example
+
+That's all there is to it. None of the actual expression output logic is
+implemented in this class. It merely serves as a selector for choosing
+a particular format. The algorithms for printing expressions in the new
+format are implemented as print methods, as described above.
+
+@code{print_myformat} is a subclass of @code{print_dflt}, so it behaves
+exactly like GiNaC's default output format:
+
+@example
@{
- symbol v("v"), c("c");
-
- ex gamma = 1/sqrt(1 - pow(v/c,2));
- ex mass_nonrel = gamma.series(v==0, 10);
-
- cout << "the relativistic mass increase with v is " << endl
- << mass_nonrel << endl;
+ symbol x("x");
+ ex e = pow(x, 2) + 1;
+
+ // this prints "1+x^2"
+ cout << e << endl;
- cout << "the inverse square of this series is " << endl
- << pow(mass_nonrel,-2).series(v==0, 10) << endl;
+ // this also prints "1+x^2"
+ e.print(print_myformat()); cout << endl;
+
+ ...
@}
@end example
-Only calling the series method makes the last output simplify to
-@math{1-v^2/c^2+O(v^10)}, without that call we would just have a long
-series raised to the power @math{-2}.
-
-@cindex M@'echain's formula
-As another instructive application, let us calculate the numerical
-value of Archimedes' constant
-@tex
-$\pi$
-@end tex
-(for which there already exists the built-in constant @code{Pi})
-using M@'echain's amazing formula
-@tex
-$\pi=16$~atan~$\!\left(1 \over 5 \right)-4$~atan~$\!\left(1 \over 239 \right)$.
-@end tex
-@ifnottex
-@math{Pi==16*atan(1/5)-4*atan(1/239)}.
-@end ifnottex
-We may expand the arcus tangent around @code{0} and insert the fractions
-@code{1/5} and @code{1/239}. But, as we have seen, a series in GiNaC
-carries an order term with it and the question arises what the system is
-supposed to do when the fractions are plugged into that order term. The
-solution is to use the function @code{series_to_poly()} to simply strip
-the order term off:
+To fill @code{print_myformat} with life, we need to supply appropriate
+print methods with @code{set_print_func()}, like this:
@example
-#include <ginac/ginac.h>
-using namespace GiNaC;
-
-ex mechain_pi(int degr)
+// This prints powers with '**' instead of '^'. See the LaTeX output
+// example above for explanations.
+void print_power_as_myformat(const power & p,
+ const print_myformat & c,
+ unsigned level)
@{
- symbol x;
- ex pi_expansion = series_to_poly(atan(x).series(x,degr));
- ex pi_approx = 16*pi_expansion.subs(x==numeric(1,5))
- -4*pi_expansion.subs(x==numeric(1,239));
- return pi_approx;
+ unsigned power_prec = p.precedence();
+ if (level >= power_prec)
+ c.s << '(';
+ p.op(0).print(c, power_prec);
+ c.s << "**";
+ p.op(1).print(c, power_prec);
+ if (level >= power_prec)
+ c.s << ')';
@}
-int main()
@{
- using std::cout; // just for fun, another way of...
- using std::endl; // ...dealing with this namespace std.
- ex pi_frac;
- for (int i=2; i<12; i+=2) @{
- pi_frac = mechain_pi(i);
- cout << i << ":\t" << pi_frac << endl
- << "\t" << pi_frac.evalf() << endl;
- @}
- return 0;
-@}
-@end example
+ ...
+ // install a new print method for power objects
+ set_print_func<power, print_myformat>(print_power_as_myformat);
-Note how we just called @code{.series(x,degr)} instead of
-@code{.series(x==0,degr)}. This is a simple shortcut for @code{ex}'s
-method @code{series()}: if the first argument is a symbol the expression
-is expanded in that symbol around point @code{0}. When you run this
-program, it will type out:
+ // now this prints "1+x**2"
+ e.print(print_myformat()); cout << endl;
-@example
-2: 3804/1195
- 3.1832635983263598326
-4: 5359397032/1706489875
- 3.1405970293260603143
-6: 38279241713339684/12184551018734375
- 3.141621029325034425
-8: 76528487109180192540976/24359780855939418203125
- 3.141591772182177295
-10: 327853873402258685803048818236/104359128170408663038552734375
- 3.1415926824043995174
+ // but the default format is still "1+x^2"
+ cout << e << endl;
+@}
@end example
-@node Built-in Functions, Input/Output, Series Expansion, Methods and Functions
+@node Structures, Adding classes, Printing, Extending GiNaC
@c node-name, next, previous, up
-@section Predefined mathematical functions
-
-GiNaC contains the following predefined mathematical functions:
-
-@cartouche
-@multitable @columnfractions .30 .70
-@item @strong{Name} @tab @strong{Function}
-@item @code{abs(x)}
-@tab absolute value
-@item @code{csgn(x)}
-@tab complex sign
-@item @code{sqrt(x)}
-@tab square root (not a GiNaC function proper but equivalent to @code{pow(x, numeric(1, 2)})
-@item @code{sin(x)}
-@tab sine
-@item @code{cos(x)}
-@tab cosine
-@item @code{tan(x)}
-@tab tangent
-@item @code{asin(x)}
-@tab inverse sine
-@item @code{acos(x)}
-@tab inverse cosine
-@item @code{atan(x)}
-@tab inverse tangent
-@item @code{atan2(y, x)}
-@tab inverse tangent with two arguments
-@item @code{sinh(x)}
-@tab hyperbolic sine
-@item @code{cosh(x)}
-@tab hyperbolic cosine
-@item @code{tanh(x)}
-@tab hyperbolic tangent
-@item @code{asinh(x)}
-@tab inverse hyperbolic sine
-@item @code{acosh(x)}
-@tab inverse hyperbolic cosine
-@item @code{atanh(x)}
-@tab inverse hyperbolic tangent
-@item @code{exp(x)}
-@tab exponential function
-@item @code{log(x)}
-@tab natural logarithm
-@item @code{Li2(x)}
-@tab Dilogarithm
-@item @code{zeta(x)}
-@tab Riemann's zeta function
-@item @code{zeta(n, x)}
-@tab derivatives of Riemann's zeta function
-@item @code{tgamma(x)}
-@tab Gamma function
-@item @code{lgamma(x)}
-@tab logarithm of Gamma function
-@item @code{beta(x, y)}
-@tab Beta function (@code{tgamma(x)*tgamma(y)/tgamma(x+y)})
-@item @code{psi(x)}
-@tab psi (digamma) function
-@item @code{psi(n, x)}
-@tab derivatives of psi function (polygamma functions)
-@item @code{factorial(n)}
-@tab factorial function
-@item @code{binomial(n, m)}
-@tab binomial coefficients
-@item @code{Order(x)}
-@tab order term function in truncated power series
-@item @code{Derivative(x, l)}
-@tab inert partial differentiation operator (used internally)
-@end multitable
-@end cartouche
+@section Structures
-@cindex branch cut
-For functions that have a branch cut in the complex plane GiNaC follows
-the conventions for C++ as defined in the ANSI standard as far as
-possible. In particular: the natural logarithm (@code{log}) and the
-square root (@code{sqrt}) both have their branch cuts running along the
-negative real axis where the points on the axis itself belong to the
-upper part (i.e. continuous with quadrant II). The inverse
-trigonometric and hyperbolic functions are not defined for complex
-arguments by the C++ standard, however. In GiNaC we follow the
-conventions used by CLN, which in turn follow the carefully designed
-definitions in the Common Lisp standard. It should be noted that this
-convention is identical to the one used by the C99 standard and by most
-serious CAS. It is to be expected that future revisions of the C++
-standard incorporate these functions in the complex domain in a manner
-compatible with C99.
+If you are doing some very specialized things with GiNaC, or if you just
+need some more organized way to store data in your expressions instead of
+anonymous lists, you may want to implement your own algebraic classes.
+('algebraic class' means any class directly or indirectly derived from
+@code{basic} that can be used in GiNaC expressions).
+GiNaC offers two ways of accomplishing this: either by using the
+@code{structure<T>} template class, or by rolling your own class from
+scratch. This section will discuss the @code{structure<T>} template which
+is easier to use but more limited, while the implementation of custom
+GiNaC classes is the topic of the next section. However, you may want to
+read both sections because many common concepts and member functions are
+shared by both concepts, and it will also allow you to decide which approach
+is most suited to your needs.
-@node Input/Output, Extending GiNaC, Built-in Functions, Methods and Functions
-@c node-name, next, previous, up
-@section Input and output of expressions
-@cindex I/O
+The @code{structure<T>} template, defined in the GiNaC header file
+@file{structure.h}, wraps a type that you supply (usually a C++ @code{struct}
+or @code{class}) into a GiNaC object that can be used in expressions.
-@subsection Expression output
-@cindex printing
-@cindex output of expressions
+@subsection Example: scalar products
-The easiest way to print an expression is to write it to a stream:
+Let's suppose that we need a way to handle some kind of abstract scalar
+product of the form @samp{<x|y>} in expressions. Objects of the scalar
+product class have to store their left and right operands, which can in turn
+be arbitrary expressions. Here is a possible way to represent such a
+product in a C++ @code{struct}:
@example
-@{
- symbol x("x");
- ex e = 4.5+pow(x,2)*3/2;
- cout << e << endl; // prints '4.5+3/2*x^2'
- // ...
-@end example
+#include <iostream>
+using namespace std;
-The output format is identical to the @command{ginsh} input syntax and
-to that used by most computer algebra systems, but not directly pastable
-into a GiNaC C++ program (note that in the above example, @code{pow(x,2)}
-is printed as @samp{x^2}).
+#include <ginac/ginac.h>
+using namespace GiNaC;
-To print an expression in a way that can be directly used in a C or C++
-program, you use the method
+struct sprod_s @{
+ ex left, right;
-@example
-void ex::printcsrc(ostream & os, unsigned type, const char *name);
+ sprod_s() @{@}
+ sprod_s(ex l, ex r) : left(l), right(r) @{@}
+@};
@end example
-This outputs a line in the form of a variable definition @code{<type> <name> = <expression>}.
-The possible types are defined in @file{ginac/flags.h} (@code{csrc_types})
-and mostly affect the way in which floating point numbers are written:
+The default constructor is required. Now, to make a GiNaC class out of this
+data structure, we need only one line:
@example
- // ...
- e.printcsrc(cout, csrc_types::ctype_float, "f");
- e.printcsrc(cout, csrc_types::ctype_double, "d");
- e.printcsrc(cout, csrc_types::ctype_cl_N, "n");
- // ...
+typedef structure<sprod_s> sprod;
@end example
-The above example will produce (note the @code{x^2} being converted to @code{x*x}):
+That's it. This line constructs an algebraic class @code{sprod} which
+contains objects of type @code{sprod_s}. We can now use @code{sprod} in
+expressions like any other GiNaC class:
@example
-float f = (3.000000e+00/2.000000e+00)*(x*x)+4.500000e+00;
-double d = (3.000000e+00/2.000000e+00)*(x*x)+4.500000e+00;
-cl_N n = (cl_F("3.0")/cl_F("2.0"))*(x*x)+cl_F("4.5");
+...
+ symbol a("a"), b("b");
+ ex e = sprod(sprod_s(a, b));
+...
@end example
-Finally, there are the two methods @code{printraw()} and @code{printtree()} intended for GiNaC
-developers, that provide a dump of the internal structure of an expression for
-debugging purposes:
+Note the difference between @code{sprod} which is the algebraic class, and
+@code{sprod_s} which is the unadorned C++ structure containing the @code{left}
+and @code{right} data members. As shown above, an @code{sprod} can be
+constructed from an @code{sprod_s} object.
+
+If you find the nested @code{sprod(sprod_s())} constructor too unwieldy,
+you could define a little wrapper function like this:
@example
- // ...
- e.printraw(cout); cout << endl << endl;
- e.printtree(cout);
+inline ex make_sprod(ex left, ex right)
+@{
+ return sprod(sprod_s(left, right));
@}
@end example
-produces
+The @code{sprod_s} object contained in @code{sprod} can be accessed with
+the GiNaC @code{ex_to<>()} function followed by the @code{->} operator or
+@code{get_struct()}:
@example
-ex(+((power(ex(symbol(name=x,serial=1,hash=150875740,flags=11)),ex(numeric(2)),hash=2,flags=3),numeric(3/2)),,hash=0,flags=3))
-
-type=Q25GiNaC3add, hash=0 (0x0), flags=3, nops=2
- power: hash=2 (0x2), flags=3
- x (symbol): serial=1, hash=150875740 (0x8fe2e5c), flags=11
- 2 (numeric): hash=2147483714 (0x80000042), flags=11
- 3/2 (numeric): hash=2147483745 (0x80000061), flags=11
- -----
- overall_coeff
- 4.5L0 (numeric): hash=2147483723 (0x8000004b), flags=11
- =====
+...
+ cout << ex_to<sprod>(e)->left << endl;
+ // -> a
+ cout << ex_to<sprod>(e).get_struct().right << endl;
+ // -> b
+...
@end example
-The @code{printtree()} method is also available in @command{ginsh} as the
-@code{print()} function.
-
-
-@subsection Expression input
-@cindex input of expressions
-
-GiNaC provides no way to directly read an expression from a stream because
-you will usually want the user to be able to enter something like @samp{2*x+sin(y)}
-and have the @samp{x} and @samp{y} correspond to the symbols @code{x} and
-@code{y} you defined in your program and there is no way to specify the
-desired symbols to the @code{>>} stream input operator.
+You only have read access to the members of @code{sprod_s}.
-Instead, GiNaC lets you construct an expression from a string, specifying the
-list of symbols to be used:
+The type definition of @code{sprod} is enough to write your own algorithms
+that deal with scalar products, for example:
@example
+ex swap_sprod(ex p)
@{
- symbol x("x"), y("y");
- ex e("2*x+sin(y)", lst(x, y));
+ if (is_a<sprod>(p)) @{
+ const sprod_s & sp = ex_to<sprod>(p).get_struct();
+ return make_sprod(sp.right, sp.left);
+ @} else
+ return p;
@}
+
+...
+ f = swap_sprod(e);
+ // f is now <b|a>
+...
@end example
-The input syntax is the same as that used by @command{ginsh} and the stream
-output operator @code{<<}. The symbols in the string are matched by name to
-the symbols in the list and if GiNaC encounters a symbol not specified in
-the list it will throw an exception.
+@subsection Structure output
-With this constructor, it's also easy to implement interactive GiNaC programs:
+While the @code{sprod} type is useable it still leaves something to be
+desired, most notably proper output:
@example
-#include <iostream>
-#include <string>
-#include <stdexcept>
-#include <ginac/ginac.h>
-using namespace std;
-using namespace GiNaC;
-
-int main()
-@{
- symbol x("x");
- string s;
-
- cout << "Enter an expression containing 'x': ";
- getline(cin, s);
-
- try @{
- ex e(s, lst(x));
- cout << "The derivative of " << e << " with respect to x is ";
- cout << e.diff(x) << ".\n";
- @} catch (exception &p) @{
- cerr << p.what() << endl;
- @}
-@}
+...
+ cout << e << endl;
+ // -> [structure object]
+...
@end example
+By default, any structure types you define will be printed as
+@samp{[structure object]}. To override this you can either specialize the
+template's @code{print()} member function, or specify print methods with
+@code{set_print_func<>()}, as described in @ref{Printing}. Unfortunately,
+it's not possible to supply class options like @code{print_func<>()} to
+structures, so for a self-contained structure type you need to resort to
+overriding the @code{print()} function, which is also what we will do here.
-@subsection Archiving
-@cindex @code{archive} (class)
-@cindex archiving
-
-GiNaC allows creating @dfn{archives} of expressions which can be stored
-to or retrieved from files. To create an archive, you declare an object
-of class @code{archive} and archive expressions in it, giving each
-expression a unique name:
+The member functions of GiNaC classes are described in more detail in the
+next section, but it shouldn't be hard to figure out what's going on here:
@example
-#include <fstream>
-using namespace std;
-#include <ginac/ginac.h>
-using namespace GiNaC;
-
-int main()
+void sprod::print(const print_context & c, unsigned level) const
@{
- symbol x("x"), y("y"), z("z");
+ // tree debug output handled by superclass
+ if (is_a<print_tree>(c))
+ inherited::print(c, level);
- ex foo = sin(x + 2*y) + 3*z + 41;
- ex bar = foo + 1;
+ // get the contained sprod_s object
+ const sprod_s & sp = get_struct();
- archive a;
- a.archive_ex(foo, "foo");
- a.archive_ex(bar, "the second one");
- // ...
+ // print_context::s is a reference to an ostream
+ c.s << "<" << sp.left << "|" << sp.right << ">";
+@}
@end example
-The archive can then be written to a file:
+Now we can print expressions containing scalar products:
@example
- // ...
- ofstream out("foobar.gar");
- out << a;
- out.close();
- // ...
+...
+ cout << e << endl;
+ // -> <a|b>
+ cout << swap_sprod(e) << endl;
+ // -> <b|a>
+...
@end example
-The file @file{foobar.gar} contains all information that is needed to
-reconstruct the expressions @code{foo} and @code{bar}.
-
-@cindex @command{viewgar}
-The tool @command{viewgar} that comes with GiNaC can be used to view
-the contents of GiNaC archive files:
-
-@example
-$ viewgar foobar.gar
-foo = 41+sin(x+2*y)+3*z
-the second one = 42+sin(x+2*y)+3*z
-@end example
+@subsection Comparing structures
-The point of writing archive files is of course that they can later be
-read in again:
+The @code{sprod} class defined so far still has one important drawback: all
+scalar products are treated as being equal because GiNaC doesn't know how to
+compare objects of type @code{sprod_s}. This can lead to some confusing
+and undesired behavior:
@example
- // ...
- archive a2;
- ifstream in("foobar.gar");
- in >> a2;
- // ...
+...
+ cout << make_sprod(a, b) - make_sprod(a*a, b*b) << endl;
+ // -> 0
+ cout << make_sprod(a, b) + make_sprod(a*a, b*b) << endl;
+ // -> 2*<a|b> or 2*<a^2|b^2> (which one is undefined)
+...
@end example
-And the stored expressions can be retrieved by their name:
+To remedy this, we first need to define the operators @code{==} and @code{<}
+for objects of type @code{sprod_s}:
@example
- // ...
- lst syms(x, y);
-
- ex ex1 = a2.unarchive_ex(syms, "foo");
- ex ex2 = a2.unarchive_ex(syms, "the second one");
+inline bool operator==(const sprod_s & lhs, const sprod_s & rhs)
+@{
+ return lhs.left.is_equal(rhs.left) && lhs.right.is_equal(rhs.right);
+@}
- cout << ex1 << endl; // prints "41+sin(x+2*y)+3*z"
- cout << ex2 << endl; // prints "42+sin(x+2*y)+3*z"
- cout << ex1.subs(x == 2) << endl; // prints "41+sin(2+2*y)+3*z"
+inline bool operator<(const sprod_s & lhs, const sprod_s & rhs)
+@{
+ return lhs.left.compare(rhs.left) < 0 ? true : lhs.right.compare(rhs.right) < 0;
@}
@end example
-Note that you have to supply a list of the symbols which are to be inserted
-in the expressions. Symbols in archives are stored by their name only and
-if you don't specify which symbols you have, unarchiving the expression will
-create new symbols with that name. E.g. if you hadn't included @code{x} in
-the @code{syms} list above, the @code{ex1.subs(x == 2)} statement would
-have had no effect because the @code{x} in @code{ex1} would have been a
-different symbol than the @code{x} which was defined at the beginning of
-the program, altough both would appear as @samp{x} when printed.
-
-
-
-@node Extending GiNaC, What does not belong into GiNaC, Input/Output, Top
-@c node-name, next, previous, up
-@chapter Extending GiNaC
+The ordering established by the @code{<} operator doesn't have to make any
+algebraic sense, but it needs to be well defined. Note that we can't use
+expressions like @code{lhs.left == rhs.left} or @code{lhs.left < rhs.left}
+in the implementation of these operators because they would construct
+GiNaC @code{relational} objects which in the case of @code{<} do not
+establish a well defined ordering (for arbitrary expressions, GiNaC can't
+decide which one is algebraically 'less').
-By reading so far you should have gotten a fairly good understanding of
-GiNaC's design-patterns. From here on you should start reading the
-sources. All we can do now is issue some recommendations how to tackle
-GiNaC's many loose ends in order to fulfill everybody's dreams. If you
-develop some useful extension please don't hesitate to contact the GiNaC
-authors---they will happily incorporate them into future versions.
+Next, we need to change our definition of the @code{sprod} type to let
+GiNaC know that an ordering relation exists for the embedded objects:
-@menu
-* What does not belong into GiNaC:: What to avoid.
-* Symbolic functions:: Implementing symbolic functions.
-* Adding classes:: Defining new algebraic classes.
-@end menu
+@example
+typedef structure<sprod_s, compare_std_less> sprod;
+@end example
+@code{sprod} objects then behave as expected:
-@node What does not belong into GiNaC, Symbolic functions, Extending GiNaC, Extending GiNaC
-@c node-name, next, previous, up
-@section What doesn't belong into GiNaC
+@example
+...
+ cout << make_sprod(a, b) - make_sprod(a*a, b*b) << endl;
+ // -> <a|b>-<a^2|b^2>
+ cout << make_sprod(a, b) + make_sprod(a*a, b*b) << endl;
+ // -> <a|b>+<a^2|b^2>
+ cout << make_sprod(a, b) - make_sprod(a, b) << endl;
+ // -> 0
+ cout << make_sprod(a, b) + make_sprod(a, b) << endl;
+ // -> 2*<a|b>
+...
+@end example
-@cindex @command{ginsh}
-First of all, GiNaC's name must be read literally. It is designed to be
-a library for use within C++. The tiny @command{ginsh} accompanying
-GiNaC makes this even more clear: it doesn't even attempt to provide a
-language. There are no loops or conditional expressions in
-@command{ginsh}, it is merely a window into the library for the
-programmer to test stuff (or to show off). Still, the design of a
-complete CAS with a language of its own, graphical capabilites and all
-this on top of GiNaC is possible and is without doubt a nice project for
-the future.
+The @code{compare_std_less} policy parameter tells GiNaC to use the
+@code{std::less} and @code{std::equal_to} functors to compare objects of
+type @code{sprod_s}. By default, these functors forward their work to the
+standard @code{<} and @code{==} operators, which we have overloaded.
+Alternatively, we could have specialized @code{std::less} and
+@code{std::equal_to} for class @code{sprod_s}.
-There are many built-in functions in GiNaC that do not know how to
-evaluate themselves numerically to a precision declared at runtime
-(using @code{Digits}). Some may be evaluated at certain points, but not
-generally. This ought to be fixed. However, doing numerical
-computations with GiNaC's quite abstract classes is doomed to be
-inefficient. For this purpose, the underlying foundation classes
-provided by @acronym{CLN} are much better suited.
+GiNaC provides two other comparison policies for @code{structure<T>}
+objects: the default @code{compare_all_equal}, and @code{compare_bitwise}
+which does a bit-wise comparison of the contained @code{T} objects.
+This should be used with extreme care because it only works reliably with
+built-in integral types, and it also compares any padding (filler bytes of
+undefined value) that the @code{T} class might have.
+@subsection Subexpressions
-@node Symbolic functions, Adding classes, What does not belong into GiNaC, Extending GiNaC
-@c node-name, next, previous, up
-@section Symbolic functions
+Our scalar product class has two subexpressions: the left and right
+operands. It might be a good idea to make them accessible via the standard
+@code{nops()} and @code{op()} methods:
-The easiest and most instructive way to start with is probably to
-implement your own function. GiNaC's functions are objects of class
-@code{function}. The preprocessor is then used to convert the function
-names to objects with a corresponding serial number that is used
-internally to identify them. You usually need not worry about this
-number. New functions may be inserted into the system via a kind of
-`registry'. It is your responsibility to care for some functions that
-are called when the user invokes certain methods. These are usual
-C++-functions accepting a number of @code{ex} as arguments and returning
-one @code{ex}. As an example, if we have a look at a simplified
-implementation of the cosine trigonometric function, we first need a
-function that is called when one wishes to @code{eval} it. It could
-look something like this:
-
-@example
-static ex cos_eval_method(const ex & x)
+@example
+size_t sprod::nops() const
@{
- // if (!x%(2*Pi)) return 1
- // if (!x%Pi) return -1
- // if (!x%Pi/2) return 0
- // care for other cases...
- return cos(x).hold();
+ return 2;
@}
-@end example
-@cindex @code{hold()}
-@cindex evaluation
-The last line returns @code{cos(x)} if we don't know what else to do and
-stops a potential recursive evaluation by saying @code{.hold()}, which
-sets a flag to the expression signaling that it has been evaluated. We
-should also implement a method for numerical evaluation and since we are
-lazy we sweep the problem under the rug by calling someone else's
-function that does so, in this case the one in class @code{numeric}:
-
-@example
-static ex cos_evalf(const ex & x)
+ex sprod::op(size_t i) const
@{
- return cos(ex_to_numeric(x));
+ switch (i) @{
+ case 0:
+ return get_struct().left;
+ case 1:
+ return get_struct().right;
+ default:
+ throw std::range_error("sprod::op(): no such operand");
+ @}
@}
@end example
-Differentiation will surely turn up and so we need to tell @code{cos}
-what the first derivative is (higher derivatives (@code{.diff(x,3)} for
-instance are then handled automatically by @code{basic::diff} and
-@code{ex::diff}):
+Implementing @code{nops()} and @code{op()} for container types such as
+@code{sprod} has two other nice side effects:
+
+@itemize @bullet
+@item
+@code{has()} works as expected
+@item
+GiNaC generates better hash keys for the objects (the default implementation
+of @code{calchash()} takes subexpressions into account)
+@end itemize
+
+@cindex @code{let_op()}
+There is a non-const variant of @code{op()} called @code{let_op()} that
+allows replacing subexpressions:
@example
-static ex cos_deriv(const ex & x, unsigned diff_param)
+ex & sprod::let_op(size_t i)
@{
- return -sin(x);
+ // every non-const member function must call this
+ ensure_if_modifiable();
+
+ switch (i) @{
+ case 0:
+ return get_struct().left;
+ case 1:
+ return get_struct().right;
+ default:
+ throw std::range_error("sprod::let_op(): no such operand");
+ @}
@}
@end example
-@cindex product rule
-The second parameter is obligatory but uninteresting at this point. It
-specifies which parameter to differentiate in a partial derivative in
-case the function has more than one parameter and its main application
-is for correct handling of the chain rule. For Taylor expansion, it is
-enough to know how to differentiate. But if the function you want to
-implement does have a pole somewhere in the complex plane, you need to
-write another method for Laurent expansion around that point.
+Once we have provided @code{let_op()} we also get @code{subs()} and
+@code{map()} for free. In fact, every container class that returns a non-null
+@code{nops()} value must either implement @code{let_op()} or provide custom
+implementations of @code{subs()} and @code{map()}.
-Now that all the ingredients for @code{cos} have been set up, we need
-to tell the system about it. This is done by a macro and we are not
-going to descibe how it expands, please consult your preprocessor if you
-are curious:
+In turn, the availability of @code{map()} enables the recursive behavior of a
+couple of other default method implementations, in particular @code{evalf()},
+@code{evalm()}, @code{normal()}, @code{diff()} and @code{expand()}. Although
+we probably want to provide our own version of @code{expand()} for scalar
+products that turns expressions like @samp{<a+b|c>} into @samp{<a|c>+<b|c>}.
+This is left as an exercise for the reader.
-@example
-REGISTER_FUNCTION(cos, eval_func(cos_eval).
- evalf_func(cos_evalf).
- derivative_func(cos_deriv));
-@end example
-
-The first argument is the function's name used for calling it and for
-output. The second binds the corresponding methods as options to this
-object. Options are separated by a dot and can be given in an arbitrary
-order. GiNaC functions understand several more options which are always
-specified as @code{.option(params)}, for example a method for series
-expansion @code{.series_func(cos_series)}. Again, if no series
-expansion method is given, GiNaC defaults to simple Taylor expansion,
-which is correct if there are no poles involved as is the case for the
-@code{cos} function. The way GiNaC handles poles in case there are any
-is best understood by studying one of the examples, like the Gamma
-(@code{tgamma}) function for instance. (In essence the function first
-checks if there is a pole at the evaluation point and falls back to
-Taylor expansion if there isn't. Then, the pole is regularized by some
-suitable transformation.) Also, the new function needs to be declared
-somewhere. This may also be done by a convenient preprocessor macro:
+The @code{structure<T>} template defines many more member functions that
+you can override by specialization to customize the behavior of your
+structures. You are referred to the next section for a description of
+some of these (especially @code{eval()}). There is, however, one topic
+that shall be addressed here, as it demonstrates one peculiarity of the
+@code{structure<T>} template: archiving.
+
+@subsection Archiving structures
+
+If you don't know how the archiving of GiNaC objects is implemented, you
+should first read the next section and then come back here. You're back?
+Good.
+
+To implement archiving for structures it is not enough to provide
+specializations for the @code{archive()} member function and the
+unarchiving constructor (the @code{unarchive()} function has a default
+implementation). You also need to provide a unique name (as a string literal)
+for each structure type you define. This is because in GiNaC archives,
+the class of an object is stored as a string, the class name.
+
+By default, this class name (as returned by the @code{class_name()} member
+function) is @samp{structure} for all structure classes. This works as long
+as you have only defined one structure type, but if you use two or more you
+need to provide a different name for each by specializing the
+@code{get_class_name()} member function. Here is a sample implementation
+for enabling archiving of the scalar product type defined above:
@example
-DECLARE_FUNCTION_1P(cos)
+const char *sprod::get_class_name() @{ return "sprod"; @}
+
+void sprod::archive(archive_node & n) const
+@{
+ inherited::archive(n);
+ n.add_ex("left", get_struct().left);
+ n.add_ex("right", get_struct().right);
+@}
+
+sprod::structure(const archive_node & n, lst & sym_lst) : inherited(n, sym_lst)
+@{
+ n.find_ex("left", get_struct().left, sym_lst);
+ n.find_ex("right", get_struct().right, sym_lst);
+@}
@end example
-The suffix @code{_1P} stands for @emph{one parameter}. Of course, this
-implementation of @code{cos} is very incomplete and lacks several safety
-mechanisms. Please, have a look at the real implementation in GiNaC.
-(By the way: in case you are worrying about all the macros above we can
-assure you that functions are GiNaC's most macro-intense classes. We
-have done our best to avoid macros where we can.)
+Note that the unarchiving constructor is @code{sprod::structure} and not
+@code{sprod::sprod}, and that we don't need to supply an
+@code{sprod::unarchive()} function.
-@node Adding classes, A Comparison With Other CAS, Symbolic functions, Extending GiNaC
+@node Adding classes, A Comparison With Other CAS, Structures, Extending GiNaC
@c node-name, next, previous, up
@section Adding classes
-If you are doing some very specialized things with GiNaC you may find that
-you have to implement your own algebraic classes to fit your needs. This
-section will explain how to do this by giving the example of a simple
-'string' class. After reading this section you will know how to properly
-declare a GiNaC class and what the minimum required member functions are
-that you have to implement. We only cover the implementation of a 'leaf'
-class here (i.e. one that doesn't contain subexpressions). Creating a
-container class like, for example, a class representing tensor products is
-more involved but this section should give you enough information so you can
-consult the source to GiNaC's predefined classes if you want to implement
-something more complicated.
+The @code{structure<T>} template provides an way to extend GiNaC with custom
+algebraic classes that is easy to use but has its limitations, the most
+severe of which being that you can't add any new member functions to
+structures. To be able to do this, you need to write a new class definition
+from scratch.
+
+This section will explain how to implement new algebraic classes in GiNaC by
+giving the example of a simple 'string' class. After reading this section
+you will know how to properly declare a GiNaC class and what the minimum
+required member functions are that you have to implement. We only cover the
+implementation of a 'leaf' class here (i.e. one that doesn't contain
+subexpressions). Creating a container class like, for example, a class
+representing tensor products is more involved but this section should give
+you enough information so you can consult the source to GiNaC's predefined
+classes if you want to implement something more complicated.
@subsection GiNaC's run-time type information system
The disadvantage of this proprietary RTTI implementation is that there's
a little more to do when implementing new classes (C++'s RTTI works more
-or less automatic) but don't worry, most of the work is simplified by
+or less automatically) but don't worry, most of the work is simplified by
macros.
@subsection A minimalistic example
string str;
@};
-GIANC_IMPLEMENT_REGISTERED_CLASS(mystring, basic)
+GINAC_IMPLEMENT_REGISTERED_CLASS(mystring, basic)
@end example
The @code{GINAC_DECLARE_REGISTERED_CLASS} and @code{GINAC_IMPLEMENT_REGISTERED_CLASS}
source (at global scope, of course, not inside a function).
@code{GINAC_DECLARE_REGISTERED_CLASS} contains, among other things the
-declarations of the default and copy constructor, the destructor, the
-assignment operator and a couple of other functions that are required. It
-also defines a type @code{inherited} which refers to the superclass so you
-don't have to modify your code every time you shuffle around the class
-hierarchy. @code{GINAC_IMPLEMENT_REGISTERED_CLASS} implements the copy
-constructor, the destructor and the assignment operator.
-
-Now there are nine member functions we have to implement to get a working
+declarations of the default constructor and a couple of other functions that
+are required. It also defines a type @code{inherited} which refers to the
+superclass so you don't have to modify your code every time you shuffle around
+the class hierarchy. @code{GINAC_IMPLEMENT_REGISTERED_CLASS} registers the
+class with the GiNaC RTTI (there is also a
+@code{GINAC_IMPLEMENT_REGISTERED_CLASS_OPT} which allows specifying additional
+options for the class, and which we will be using instead in a few minutes).
+
+Now there are seven member functions we have to implement to get a working
class:
@itemize
@item
@code{mystring()}, the default constructor.
-@item
-@code{void destroy(bool call_parent)}, which is used in the destructor and the
-assignment operator to free dynamically allocated members. The @code{call_parent}
-specifies whether the @code{destroy()} function of the superclass is to be
-called also.
-
-@item
-@code{void copy(const mystring &other)}, which is used in the copy constructor
-and assignment operator to copy the member variables over from another
-object of the same class.
-
@item
@code{void archive(archive_node &n)}, the archiving function. This stores all
information needed to reconstruct an object of this class inside an
@code{archive_node}.
@item
-@code{mystring(const archive_node &n, const lst &sym_lst)}, the unarchiving
+@code{mystring(const archive_node &n, lst &sym_lst)}, the unarchiving
constructor. This constructs an instance of the class from the information
found in an @code{archive_node}.
@item
-@code{ex unarchive(const archive_node &n, const lst &sym_lst)}, the static
+@code{ex unarchive(const archive_node &n, lst &sym_lst)}, the static
unarchiving function. It constructs a new instance by calling the unarchiving
constructor.
@item
+@cindex @code{compare_same_type()}
@code{int compare_same_type(const basic &other)}, which is used internally
by GiNaC to establish a canonical sort order for terms. It returns 0, +1 or
-1, depending on the relative order of this object and the @code{other}
Let's proceed step-by-step. The default constructor looks like this:
@example
-mystring::mystring() : inherited(TINFO_mystring)
-@{
- // dynamically allocate resources here if required
-@}
+mystring::mystring() : inherited(TINFO_mystring) @{@}
@end example
The golden rule is that in all constructors you have to set the
it will be set by the constructor of the superclass and all hell will break
loose in the RTTI. For your convenience, the @code{basic} class provides
a constructor that takes a @code{tinfo_key} value, which we are using here
-(remember that in our case @code{inherited = basic}). If the superclass
+(remember that in our case @code{inherited == basic}). If the superclass
didn't have such a constructor, we would have to set the @code{tinfo_key}
to the right value manually.
In the default constructor you should set all other member variables to
reasonable default values (we don't need that here since our @code{str}
-member gets set to an empty string automatically). The constructor(s) are of
-course also the right place to allocate any dynamic resources you require.
-
-Next, the @code{destroy()} function:
-
-@example
-void mystring::destroy(bool call_parent)
-@{
- // free dynamically allocated resources here if required
- if (call_parent)
- inherited::destroy(call_parent);
-@}
-@end example
-
-This function is where we free all dynamically allocated resources. We don't
-have any so we're not doing anything here, but if we had, for example, used
-a C-style @code{char *} to store our string, this would be the place to
-@code{delete[]} the string storage. If @code{call_parent} is true, we have
-to call the @code{destroy()} function of the superclass after we're done
-(to mimic C++'s automatic invocation of superclass destructors where
-@code{destroy()} is called from outside a destructor).
-
-The @code{copy()} function just copies over the member variables from
-another object:
-
-@example
-void mystring::copy(const mystring &other)
-@{
- inherited::copy(other);
- str = other.str;
-@}
-@end example
-
-We can simply overwrite the member variables here. There's no need to worry
-about dynamically allocated storage. The assignment operator (which is
-automatically defined by @code{GINAC_IMPLEMENT_REGISTERED_CLASS}, as you
-recall) calls @code{destroy()} before it calls @code{copy()}. You have to
-explicitly call the @code{copy()} function of the superclass here so
-all the member variables will get copied.
+member gets set to an empty string automatically).
Next are the three functions for archiving. You have to implement them even
if you don't plan to use archives, but the minimum required implementation
-is really simple. First, the archiving function:
+is really simple. First, the archiving function:
@example
void mystring::archive(archive_node &n) const
The only thing that is really required is calling the @code{archive()}
function of the superclass. Optionally, you can store all information you
deem necessary for representing the object into the passed
-@code{archive_node}. We are just storing our string here. For more
+@code{archive_node}. We are just storing our string here. For more
information on how the archiving works, consult the @file{archive.h} header
file.
function:
@example
-mystring::mystring(const archive_node &n, const lst &sym_lst) : inherited(n, sym_lst)
+mystring::mystring(const archive_node &n, lst &sym_lst) : inherited(n, sym_lst)
@{
n.find_string("string", str);
@}
Finally, the unarchiving function:
@example
-ex mystring::unarchive(const archive_node &n, const lst &sym_lst)
+ex mystring::unarchive(const archive_node &n, lst &sym_lst)
@{
return (new mystring(n, sym_lst))->setflag(status_flags::dynallocated);
@}
@end example
-You don't have to understand how exactly this works. Just copy these four
-lines into your code literally (replacing the class name, of course). It
-calls the unarchiving constructor of the class and unless you are doing
-something very special (like matching @code{archive_node}s to global
-objects) you don't need a different implementation. For those who are
-interested: setting the @code{dynallocated} flag puts the object under
-the control of GiNaC's garbage collection. It will get deleted automatically
-once it is no longer referenced.
+You don't have to understand how exactly this works. Just copy these
+four lines into your code literally (replacing the class name, of
+course). It calls the unarchiving constructor of the class and unless
+you are doing something very special (like matching @code{archive_node}s
+to global objects) you don't need a different implementation. For those
+who are interested: setting the @code{dynallocated} flag puts the object
+under the control of GiNaC's garbage collection. It will get deleted
+automatically once it is no longer referenced.
Our @code{compare_same_type()} function uses a provided function to compare
the string members:
Now the only thing missing is our two new constructors:
@example
-mystring::mystring(const string &s) : inherited(TINFO_mystring), str(s)
-@{
- // dynamically allocate resources here if required
-@}
-
-mystring::mystring(const char *s) : inherited(TINFO_mystring), str(s)
-@{
- // dynamically allocate resources here if required
-@}
+mystring::mystring(const string &s) : inherited(TINFO_mystring), str(s) @{@}
+mystring::mystring(const char *s) : inherited(TINFO_mystring), str(s) @{@}
@end example
No surprises here. We set the @code{str} member from the argument and
@example
ex e = mystring("Hello, world!");
-cout << is_ex_of_type(e, mystring) << endl;
+cout << is_a<mystring>(e) << endl;
// -> 1 (true)
cout << e.bp->class_name() << endl;
@end example
Hm, not exactly what we expect, but of course the @code{mystring} class
-doesn't yet know how to print itself. This is done in the @code{print()}
-member function. Let's say that we wanted to print the string surrounded
-by double quotes:
+doesn't yet know how to print itself. This can be done either by implementing
+the @code{print()} member function, or, preferably, by specifying a
+@code{print_func<>()} class option. Let's say that we want to print the string
+surrounded by double quotes:
@example
class mystring : public basic
@{
...
-public:
- void print(ostream &os, unsigned upper_precedence) const;
+protected:
+ void do_print(const print_context &c, unsigned level = 0) const;
...
@};
-void mystring::print(ostream &os, unsigned upper_precedence) const
+void mystring::do_print(const print_context &c, unsigned level) const
@{
- os << '\"' << str << '\"';
+ // print_context::s is a reference to an ostream
+ c.s << '\"' << str << '\"';
@}
@end example
-The @code{upper_precedence} argument is only required for container classes
-to correctly parenthesize the output. Let's try again to print the expression:
+The @code{level} argument is only required for container classes to
+correctly parenthesize the output.
+
+Now we need to tell GiNaC that @code{mystring} objects should use the
+@code{do_print()} member function for printing themselves. For this, we
+replace the line
+
+@example
+GINAC_IMPLEMENT_REGISTERED_CLASS(mystring, basic)
+@end example
+
+with
+
+@example
+GINAC_IMPLEMENT_REGISTERED_CLASS_OPT(mystring, basic,
+ print_func<print_context>(&mystring::do_print))
+@end example
+
+Let's try again to print the expression:
@example
cout << e << endl;
// -> "Hello, world!"
@end example
-Much better. The @code{mystring} class can be used in arbitrary expressions:
+Much better. If we wanted to have @code{mystring} objects displayed in a
+different way depending on the output format (default, LaTeX, etc.), we
+would have supplied multiple @code{print_func<>()} options with different
+template parameters (@code{print_dflt}, @code{print_latex}, etc.),
+separated by dots. This is similar to the way options are specified for
+symbolic functions. @xref{Printing}, for a more in-depth description of the
+way expression output is implemented in GiNaC.
+
+The @code{mystring} class can be used in arbitrary expressions:
@example
e += mystring("GiNaC rulez");
// -> "GiNaC rulez"+"Hello, world!"
@end example
-(note that GiNaC's automatic term reordering is in effect here), or even
+(GiNaC's automatic term reordering is in effect here), or even
@example
e = pow(mystring("One string"), 2*sin(Pi-mystring("Another string")));
@subsection Automatic evaluation
-@cindex @code{hold()}
@cindex evaluation
+@cindex @code{eval()}
+@cindex @code{hold()}
When dealing with objects that are just a little more complicated than the
simple string objects we have implemented, chances are that you will want to
have some automatic simplifications or canonicalizations performed on them.
@}
if (new_str.length() == 0)
- return _ex0();
+ return 0;
else
return mystring(new_str).hold();
@}
@end example
The @code{level} argument is used to limit the recursion depth of the
-evaluation. We don't have any subexpressions in the @code{mystring} class
-so we are not concerned with this. If we had, we would call the @code{eval()}
-functions of the subexpressions with @code{level - 1} as the argument if
-@code{level != 1}. The @code{hold()} member function sets a flag in the
-object that prevents further evaluation. Otherwise we might end up in an
-endless loop. When you want to return the object unmodified, use
-@code{return this->hold();}.
+evaluation. We don't have any subexpressions in the @code{mystring}
+class so we are not concerned with this. If we had, we would call the
+@code{eval()} functions of the subexpressions with @code{level - 1} as
+the argument if @code{level != 1}. The @code{hold()} member function
+sets a flag in the object that prevents further evaluation. Otherwise
+we might end up in an endless loop. When you want to return the object
+unmodified, use @code{return this->hold();}.
Let's confirm that it works:
// -> 3*"wow"
@end example
-@subsection Other member functions
+@subsection Optional member functions
We have implemented only a small set of member functions to make the class
-work in the GiNaC framework. For a real algebraic class, there are probably
-some more functions that you will want to re-implement, such as
-@code{evalf()}, @code{series()} or @code{op()}. Have a look at @file{basic.h}
-or the header file of the class you want to make a subclass of to see
-what's there. You can, of course, also add your own new member functions.
-In this case you will probably want to define a little helper function like
+work in the GiNaC framework. There are two functions that are not strictly
+required but will make operations with objects of the class more efficient:
+@cindex @code{calchash()}
+@cindex @code{is_equal_same_type()}
@example
-inline const mystring &ex_to_mystring(const ex &e)
-@{
- return static_cast<const mystring &>(*e.bp);
-@}
+unsigned calchash() const;
+bool is_equal_same_type(const basic &other) const;
+@end example
+
+The @code{calchash()} method returns an @code{unsigned} hash value for the
+object which will allow GiNaC to compare and canonicalize expressions much
+more efficiently. You should consult the implementation of some of the built-in
+GiNaC classes for examples of hash functions. The default implementation of
+@code{calchash()} calculates a hash value out of the @code{tinfo_key} of the
+class and all subexpressions that are accessible via @code{op()}.
+
+@code{is_equal_same_type()} works like @code{compare_same_type()} but only
+tests for equality without establishing an ordering relation, which is often
+faster. The default implementation of @code{is_equal_same_type()} just calls
+@code{compare_same_type()} and tests its result for zero.
+
+@subsection Other member functions
+
+For a real algebraic class, there are probably some more functions that you
+might want to provide:
+
+@example
+bool info(unsigned inf) const;
+ex evalf(int level = 0) const;
+ex series(const relational & r, int order, unsigned options = 0) const;
+ex derivative(const symbol & s) const;
+@end example
+
+If your class stores sub-expressions (see the scalar product example in the
+previous section) you will probably want to override
+
+@cindex @code{let_op()}
+@example
+size_t nops() cont;
+ex op(size_t i) const;
+ex & let_op(size_t i);
+ex subs(const lst & ls, const lst & lr, unsigned options = 0) const;
+ex map(map_function & f) const;
@end example
-that let's you get at the object inside an expression (after you have verified
-that the type is correct) so you can call member functions that are specific
-to the class.
+@code{let_op()} is a variant of @code{op()} that allows write access. The
+default implementations of @code{subs()} and @code{map()} use it, so you have
+to implement either @code{let_op()}, or @code{subs()} and @code{map()}.
+
+You can, of course, also add your own new member functions. Remember
+that the RTTI may be used to get information about what kinds of objects
+you are dealing with (the position in the class hierarchy) and that you
+can always extract the bare object from an @code{ex} by stripping the
+@code{ex} off using the @code{ex_to<mystring>(e)} function when that
+should become a need.
That's it. May the source be with you!
disadvantages over these systems.
@menu
-* Advantages:: Stengths of the GiNaC approach.
+* Advantages:: Strengths of the GiNaC approach.
* Disadvantages:: Weaknesses of the GiNaC approach.
* Why C++?:: Attractiveness of C++.
@end menu
@item
development tools: powerful development tools exist for C++, like fancy
editors (e.g. with automatic indentation and syntax highlighting),
-debuggers, visualization tools, documentation generators...
+debuggers, visualization tools, documentation generators@dots{}
@item
modularization: C++ programs can easily be split into modules by
windows into GiNaC have been implemented and many more are possible: the
tiny @command{ginsh} that is part of the distribution exposes GiNaC's
types to a command line and second, as a more consistent approach, an
-interactive interface to the @acronym{Cint} C++ interpreter has been put
-together (called @acronym{GiNaC-cint}) that allows an interactive
-scripting interface consistent with the C++ language.
+interactive interface to the Cint C++ interpreter has been put together
+(called GiNaC-cint) that allows an interactive scripting interface
+consistent with the C++ language. It is available from the usual GiNaC
+FTP-site.
@item
-seemless integration: it is somewhere between difficult and impossible
+seamless integration: it is somewhere between difficult and impossible
to call CAS functions from within a program written in C++ or any other
programming language and vice versa. With GiNaC, your symbolic routines
are part of your program. You can easily call third party libraries,
portability: While the GiNaC library itself is designed to avoid any
platform dependent features (it should compile on any ANSI compliant C++
compiler), the currently used version of the CLN library (fast large
-integer and arbitrary precision arithmetics) can be compiled only on
-systems with a recently new C++ compiler from the GNU Compiler
-Collection (@acronym{GCC}).@footnote{This is because CLN uses
-PROVIDE/REQUIRE like macros to let the compiler gather all static
-initializations, which works for GNU C++ only.} GiNaC uses recent
-language features like explicit constructors, mutable members, RTTI,
-@code{dynamic_cast}s and STL, so ANSI compliance is meant literally.
-Recent @acronym{GCC} versions starting at 2.95, although itself not yet
-ANSI compliant, support all needed features.
+integer and arbitrary precision arithmetics) can only by compiled
+without hassle on systems with the C++ compiler from the GNU Compiler
+Collection (GCC).@footnote{This is because CLN uses PROVIDE/REQUIRE like
+macros to let the compiler gather all static initializations, which
+works for GNU C++ only. Feel free to contact the authors in case you
+really believe that you need to use a different compiler. We have
+occasionally used other compilers and may be able to give you advice.}
+GiNaC uses recent language features like explicit constructors, mutable
+members, RTTI, @code{dynamic_cast}s and STL, so ANSI compliance is meant
+literally. Recent GCC versions starting at 2.95.3, although itself not
+yet ANSI compliant, support all needed features.
@end itemize
@cindex reference counting
@cindex copy-on-write
@cindex garbage collection
-An expression is extremely light-weight since internally it works like a
-handle to the actual representation and really holds nothing more than a
-pointer to some other object. What this means in practice is that
-whenever you create two @code{ex} and set the second equal to the first
-no copying process is involved. Instead, the copying takes place as soon
-as you try to change the second. Consider the simple sequence of code:
+In GiNaC, there is an @emph{intrusive reference-counting} mechanism at work
+where the counter belongs to the algebraic objects derived from class
+@code{basic} but is maintained by the smart pointer class @code{ptr}, of
+which @code{ex} contains an instance. If you understood that, you can safely
+skip the rest of this passage.
+
+Expressions are extremely light-weight since internally they work like
+handles to the actual representation. They really hold nothing more
+than a pointer to some other object. What this means in practice is
+that whenever you create two @code{ex} and set the second equal to the
+first no copying process is involved. Instead, the copying takes place
+as soon as you try to change the second. Consider the simple sequence
+of code:
@example
+#include <iostream>
#include <ginac/ginac.h>
using namespace std;
using namespace GiNaC;
can be:
@example
-#include <ginac/ginac.h>
-using namespace std;
-using namespace GiNaC;
-
-int main()
@{
symbol x("x"), y("y");
happens. Knowing this will enable you to write much more efficient
code. If you still have an uncertain feeling with copy-on-write
semantics, we recommend you have a look at the
-@uref{http://www.cerfnet.com/~mpcline/c++-faq-lite/, C++-FAQ lite} by
+@uref{http://www.parashift.com/c++-faq-lite/, C++-FAQ lite} by
Marshall Cline. Chapter 16 covers this issue and presents an
implementation which is pretty close to the one in GiNaC.
and the @samp{AM_PATH_GINAC} macro. The program used here is @file{simple.cpp}:
@example
+#include <iostream>
#include <ginac/ginac.h>
-int main(void)
+int main()
@{
GiNaC::symbol x("x");
GiNaC::ex a = GiNaC::sin(x);
AC_PROG_INSTALL
AC_LANG_CPLUSPLUS
-AM_PATH_GINAC(0.7.0, [
+AM_PATH_GINAC(0.9.0, [
LIBS="$LIBS $GINACLIB_LIBS"
CPPFLAGS="$CPPFLAGS $GINACLIB_CPPFLAGS"
], AC_MSG_ERROR([need to have GiNaC installed]))
@end example
This @file{Makefile.am}, says that we are building a single executable,
-from a single sourcefile @file{simple.cpp}. Since every program
+from a single source file @file{simple.cpp}. Since every program
we are building uses GiNaC we simply added the GiNaC options
to @env{$LIBS} and @env{$CPPFLAGS}, but in other circumstances, we might
want to specify them on a per-program basis: for instance by
@item
@cite{Computer Algebra: Systems and Algorithms for Algebraic Computation},
-J.H. Davenport, Y. Siret, and E. Tournier, ISBN 0-12-204230-1, 1988,
+James H. Davenport, Yvon Siret and Evelyne Tournier, ISBN 0-12-204230-1, 1988,
Academic Press, London
+@item
+@cite{Computer Algebra Systems - A Practical Guide},
+Michael J. Wester (editor), ISBN 0-471-98353-5, 1999, Wiley, Chichester
+
+@item
+@cite{The Art of Computer Programming, Vol 2: Seminumerical Algorithms},
+Donald E. Knuth, ISBN 0-201-89684-2, 1998, Addison Wesley
+
+@item
+@cite{Pi Unleashed}, J@"org Arndt and Christoph Haenel,
+ISBN 3-540-66572-2, 2001, Springer, Heidelberg
+
+@item
+@cite{The Role of gamma5 in Dimensional Regularization}, Dirk Kreimer, hep-ph/9401354
+
@end itemize
git://www.ginac.de / ginac.git / blobdiff