Dear Marianne,
It is not very clear for me what is the problem you try to solve. The
term Grad(uf) is a priori a vector one since the term uf is a scalar
one. May be you can clarify a bit. Moreover, in order to solve an
eigenvalue problem, you have to perform the assembly of the stiffness
matrix, the mass matrix and then search the eigenvalues.
Best regards,
Yves.
Le 05/03/2015 08:47, Marianne Petersen a écrit :
> Dear community,
>
> I am trying to implement the following problem Laplacian eigenvalue
> problem:
> \int Grad(<f,u>) dA = \lambda \int u*f dA
> with Dirichlet boundary conditions and a Neumann condition.
> Since this problem is observed on a mesh with n Triangles The equation
> is to be solved on every triangle and the corresponding fem.
>
> Is my idea of using the following expression for the lhs correct?
> getfem::mesh mymesh;
>
> // finite element method
> getfem::mesh_fem mf(mymesh);
> getfem::pfem pf = getfem::fem_descriptor("FEM_PK(2,1)");
> mf.set_finite_element(mymesh.convex_index(), pf);
>
> // integration method
> getfem::mesh_im intm(mymesh);
> getfem::pintegration_method ppi =
> getfem::int_method_descriptor("IM_TRIANGLE(7)");
> intm.set_integration_method(ppi);
>
> getfem::ga_workspace workspace;
> getfem::size_type nbdof = mf.nb_dof();
> getfem::base_vector U(nbdof);
>
> // left hand side: A
> workspace.add_fem_variable("u", mf, gmm::sub_interval(0, nbdof), U);
> workspace.add_fem_variable("f", mf, gmm::sub_interval(0, nbdof), U);
> workspace.add_expression("f.Test_u", intm);
> getfem::base_vector skalprod(nbdof);
> workspace.set_assembled_vector(skalprod);
> workspace.assembly(0);
>
> workspace.clear_expressions();
>
> workspace.add_fem_variable("skp", mf, gmm::sub_interval(0, nbdof),
> skalprod);
> workspace.add_expression("Grad_skp", intm);
> getfem::model_real_sparse_matrix A(nbdof, nbdof);
> workspace.set_assembled_matrix(A);
> workspace.assembly(2);
>
> I am really unsure about how to implement this problem.
> Do you have an idea? Or should I use the "bricks"? Although I am not
> sure either if this would work..
>
> How can I make sure that the problem is for real implemented on each
> trinagle of the mesh?
>
> Thank you already very much in advance :)
>
> Best regards
> Marianne Petersen
>
>
> _______________________________________________
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--
Yves Renard ([email protected]) tel : (33) 04.72.43.87.08
Pole de Mathematiques, INSA-Lyon fax : (33) 04.72.43.85.29
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard
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