documentation update

[ginac.git] / doc / tutorial / ginac.texi

diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi
index 2af37ad4074211a4f217e9766a3a38b1c3cc1e4b..14154336713053423bf026c67c7410ab49a35222 100644 (file)
--- a/doc/tutorial/ginac.texi
+++ b/doc/tutorial/ginac.texi
@@ -931,10 +931,22 @@ int main()
     numeric trott("1.0841015122311136151E-2");
     
     std::cout << two*p << std::endl;  // floating point 6.283...
+    ...
+@end example
+
+@cindex @code{I}
+@cindex complex numbers
+The imaginary unit in GiNaC is a predefined @code{numeric} object with the
+name @code{I}:
+
+@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 numbers writing @code{numeric r(3/2)}.
+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
@@ -4286,19 +4298,22 @@ and have the @samp{x} and @samp{y} correspond to the symbols @code{x} and
 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:
+list of symbols and indices to be used:
 
 @example
 @{
-    symbol x("x"), y("y");
-    ex e("2*x+sin(y)", lst(x, y));
+    symbol x("x"), y("y"), p("p");
+    idx i(symbol("i"), 3);
+    ex e("2*x+sin(y)+p.i", lst(x, y, p, i));
 @}
 @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.
+output operator @code{<<}. The symbols and indices in the string are matched
+by name to the symbols and indices in the list and if GiNaC encounters a
+symbol or index not specified in the list it will throw an exception. Only
+indices whose values are single symbols can be used (i.e. numeric indices
+or compound indices as in "A.(2*n+1)" are not allowed).
 
 With this constructor, it's also easy to implement interactive GiNaC programs: