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

[Iago Barbeiro]

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