syfi team mailing list archive

[kent-and@xxxxxxxxx]

> 2007/7/5, fhima@xxxxxxxxxxxxxxxxx <fhima@xxxxxxxxxxxxxxxxx>:
>> > 2007/7/5, fhima@xxxxxxxxxxxxxxxxx <fhima@xxxxxxxxxxxxxxxxx>:
>> >> > 2007/7/5, fhima@xxxxxxxxxxxxxxxxx <fhima@xxxxxxxxxxxxxxxxx>:
>> >> >> Hello Matrin,
>> >> >>
>> >> >> Can you say me please how i can
>> >> >>        *derivate fe.N(i) rwt x (first composant)
>> >> >>        *integrate on surface domaine
>> >> >>
>> >> >> Think you!
>> >> >
>> >> >
>> >> > diff( fe.N(i), x )
>> >> >
>> >> > ReferenceTetrahedron tet;
>> >> > Triangle polygon = tet.triangle(0);
>> >> > ex itg = polygon.integrate( fe.N(i) );
>> >> >
>> >> > There should be examples of this in the SyFi manual, and see also
>> the
>> >> > ginac manual for more about diff etc.
>> >> >
>> >> > Please send further questions to syfi-dev@xxxxxxxxxx
>> >> >
>> >>
>> >>
>> >> > --
>> >> > ---
>> >> > Martin Sandve Alnæs
>> >> > PhD student, Cardiac Computations
>> >> > Simula Research Laboratory, Norway
>> >> >
>> >>
>> >> Matrin,
>> >>
>> >> There are a problem because fe.N(i) is not an expression of x.
>> >> And i have not an expression of this fuction
>> >
>> > Try this code:
>> > ex x1 = symbol("x");
>> > ex x2 = symbol("x");
>> > ex f = x1-x2;
>> > cout << f;
>> >
>> > As you can see, a symbol in ginac is not identified by its name, each
>> > object is a distinct symbol. You must use the global variables x, y, z
>> > from SyFi, not create your own. Look up get_symbol in the manual.
>> >
>> > I strongly recommend going to www.ginac.de and reading the
>> > documentation, at least the basics.
>> >
>> > --
>> > ---
>> > Martin Sandve Alnæs
>> > PhD student, Cardiac Computations
>> > Simula Research Laboratory, Norway
>> >
>>
>> Matrin,
>>
>> I see the manull of ginac
>> my problem is that i want to diffenrentiate fe.N(i) but it is impossible
>> because i have not the expression of fe.N(i)
>>
>> If you have am idea to the expression of fe.N(i) then it is good for me
>>
>> Bye
>> Think you
>
>
> I don't understand your problem, fe.N(i) returns the expression you
> want. If you stil have problems you must show us the code you've tried
> to write.
>
> --
> ---
> Martin Sandve Alnæs
> PhD student, Cardiac Computations
> Simula Research Laboratory, Norway
> _______________________________________________
> SyFi-dev mailing list
> SyFi-dev@xxxxxxxxxx
> http://fenics.org/mailman/listinfo/syfi-dev
>

Isn't this what you want:


#include <ginac/ginac.h>
#include <iostream>
#include <SyFi/SyFi.h>

using namespace GiNaC;
using namespace SyFi;

int main () {

  initSyFi(3);
  ReferenceTetrahedron t;
  Lagrange fe(t,1);

  for (int i=0; i<fe.nbf(); i++) {
    ex dN = diff(fe.N(i), x);
    std::cout << "dNi(0)/dx "<<dN<<std::endl;
    ex surface_integral =  t.triangle(0).integrate(fe.N(i));
    std::cout << "surface_integral "<<surface_integral<<std::endl;
  }
}


Kent