[GiNaC-list] Re: Defining a new symbol class (mysymbol.cpp)

jros jros at unavarra.es
Wed Nov 14 14:08:10 CET 2007

> > But if I follow mystring.cpp example, and I try to change
> > 
> >   print_func<print_context>(&mystring::do_print))
> > 
> > to
> > 
> >   print_func<print_context>(&mystring::do_print))
> > 

and also

class mysymbol : public string


class mysymbol : public symbol

> This is not enough. Did you change the constructors?

I leave the constructors as they are

// ctors
mystring::mystring() : inherited(&mystring::tinfo_static) { }
mystring::mystring(const string &s) :
inherited(&mystring::tinfo_static), str(s) { }
mystring::mystring(const char *s) : inherited(&mystring::tinfo_static),
str(s) { }

then error is:

$ g++ -o mystring mystring.cpp `pkg-config --cflags --libs ginac`
mystring.cpp: In constructor ‘mystring::mystring()’:
mystring.cpp:32: error: no matching function for call to
‘GiNaC::symbol::symbol(const GiNaC::tinfo_static_t*)’

The manual implicitly suggesst that this should not be a problem, so I
were confused.

Thanks to you, I can now see that changing them to

// ctors
mystring::mystring()  { tinfo_key = MYSTRING_RTTI; }
mystring::mystring(const string &s) : str(s) { tinfo_key =
mystring::mystring(const char *s) : str(s) { tinfo_key =

It works.

I think it can be beneficial for the Tutorial (I think you are one of
the developers), more pedagogical, to define the constructors in this
way, because
I think that they will work allways in this form, and obiously the
reverse is not true, the posibility used right now calling the inherited
method could be a footnote.

Just for curiosity what does it means: // ctors, and w.r.t.

Also I see that the archiving constructor, now in your yesterday's
mysymbol.cpp, do not need to set tinfo_key


mysymbol::mysymbol(const archive_node &n, lst &sym_lst) : inherited(n,
        //tinfo_key = MYSYMBOL_RTTI;

compiles and executes OK.

Is this correct in general terms?, the manual does not say anything
about having to set tinfo_key in the archiving constructor.

Also it would be beneficial to have a second example like mysymbol.cpp
this in the tutorial, perhaps adding a numeric representing the value of
the symbol, and redefining the evalf() method so that evaluation of the
symbol uses the numeric field to compute the value, like for constants.

If the derivative overloading is maintained, It would be preferable if
it does something useful, as returning for symbol "e" the symbol "de"
that represents its derivative with respect to symbol time "t". This way
total derivatives with "t" like in clasic mechanics (my field) can be
done for expresions.

This has the drawback, that "t" should be a global variable in the
example, and "de" a mysymbol member of mysymbol, so new constructor
needed, or a mysymbol created on the fly.

I hope this helps, and again, thanks a lot.

I wan't to ask also about dealing with non-conmutativity of a defined
symbol -something that is no clear in the Tutorial- but I will postpone
the subjet.


Javier Ros

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