Re: [Getfem-users] Problems to build a matrix for a boundary term

[Renard Yves]

Dear Iago,

I think this is the term "Normal" which leads to this error (can you  
verify it ?). The normal is indeed constant for an affine geometric  
transformation but I a not sure that this term is taken into account  
for exact computations. The simplest is to use a cubature method !

Yves.



Iago Barbeiro <address@hidden> a écrit :

> Dear Ronan,
> Thanks for the prompt answer.
>
> You are right, circular domain and holes may sound higher order
> transformation, but it is not the case here.
> I'm using an affine triangular mesh, GT_PK(2,1), and also affine continuos
> shape functions FEM_PK(2,1).
> Any other clues?
>
> Regards,
>
> Iago
>
>
> 2009/9/5 Ronan Perrussel <address@hidden>
>
> > Dear Iago,
> >
> > the exact integration is mainly linked to the use of an affine mesh.
> > Is it the case here? You speak about a circular hole and maybe you use
> > second order transformation for the elements around the hole...
> >
> > I hope it helps.
> >
> > Best regards,
> > Ronan
> >
> > Iago Barbeiro a écrit :
> >
> > > Dear Getfem++ users,
> > >
> > > I am facing problems to build an elementary matrix using the generic
> > > assembly procedure and I hope anyone could give me a hand.
> > >
> > > It is a boundary integral in a two dimensional mesh (It is a circular
> > > domain with a circular hole inside and I want to integrate over both
> > > boundaries):
> > >
> > > Int[boundary]((Grad(p).normal).dp)
> > >
> > > So it is a bilinear form in "p" and "dp" where both are scalars defined
> > > with the same fem (mf_p).
> > >
> > > For that I have tried the following block:
> > >
> > > *template<typename MAT> *
> > > *void asm_P_Lap_boundary(const MAT &K_,*
> > > * **                   const mesh_im &mim,*
> > > * **                   const mesh_fem &mf_p, *
> > > * **                   const mesh_region &rg) {*
> > > *
> > > *
> > > *     MAT &K = const_cast<MAT &>(K_);*
> > > *
> > > *
> > > *     getfem::generic_assembly assem;*
> > > *   *
> > > *     assem.set("M(#1,#1)+=comp(Grad(#1).Normal().Base(#1))(:,i,i,:);");*
> > > *          *
> > > *     assem.push_mi(mim);*
> > > *     assem.push_mf(mf_p);*
> > > *     assem.push_mat(K);*
> > > *     assem.assembly(rg);*
> > > * }*
> > >
> > > Where the mesh_region was built using:
> > >
> > > *getfem::mesh_region boundary;*
> > > *getfem::outer_faces_of_mesh(mymesh, boundary);*
> > >
> > > But then I found an error message, which is:
> > >
> > > *============================================*
> > > *|      An error has been detected !!!      |*
> > > *============================================*
> > > *Error in getfem_mat_elem.cc, line 121 : *
> > > *Exact integration not allowed in this context*
> > >
> > > Why exact integration would not be allowed here? Am I doing something
> > > wrong? Any light?
> > >
> > > Thanks for your attention!
> > >
> > > Iago C. Barbeiro
> > > ------------------------------------------------------------------------
> > >
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