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

From: Iago Barbeiro
Subject: Re: [Getfem-users] Problems to build a matrix for a boundary term
Date: Sat, 5 Sep 2009 09:59:36 -0300

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?



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,

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):


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, 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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