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Re: [Getfem-users] getFem problem, export bug possibly and mailing list

From: Renard Yves
Subject: Re: [Getfem-users] getFem problem, export bug possibly and mailing list issue
Date: Sun, 12 Jul 2009 13:35:14 +0200
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Umut Tabak <address@hidden> a écrit :

Dear Professor Renard,

First, of all, I would like let you know, that I am registered for the Getfem users mailing list, but none of my posts appear on the mailing list pages on the gna server. I confirmed my membership but as said, my messages do not appear online. Do you have any idea what I should do.

This is probably because you use a different mail address than the one you give to register yourself.

I have 1 question and possibly one inconsistency in the matrix market export of the matrices that are formed by the getFem++.

1.) I am trying to use the library for my Ph.D. research project in order to assemble my system matrices (For the moment I am concerned with interior vibroacoustic problems so I need the assemble the structural and fluid parts of the matrices as well as the coupling terms which result in an unsymmetric system, most probably, you are familiar with this problem). I followed the documentation and could assemble some matrices for the solution of the helmholtz equation on a, say, 3d domain where I import the mesh from Gmsh. This type of problem is a scalar problem since only the pressures are the unknowns. I set the dimension of the mesh to 1 with the set_qdim() method and use FEM_QK(3,1) without problems, though the mesh is 3D but with set_qdim(1) I can get the right results which I could nor understand.

If I try to use the linear elasticity assemble function on page 27 on the manual, namely, asm_stiffness_matrix_for_linear_elasticity, with mesh dimension 1, I get a wrong qdim error for the mesh_fem, if I use set_qdim(3) and for instance with FEM_PK(3,1) and IM_TETRAHEDRON(5) I get

Error in /usr/local/include/getfem/getfem_assembling.h, line 577 :
invalid data mesh fem (Qdim=1 required)

This means that you give the elasticity coefficients on a vectorial fem. You need two fems to call this assembly procedure a first one for the unknown which as to be vectorial (set_qdim(N)) and a second one, which is often a P0 method if your coefficients are constant, to describe the Lamé coefficients. Note that in the current devloppement version (you can get via there is an assembly procedure, namely asm_stiffness_matrix_for_homogeneous_linear_elasticity which does not require a fem for the lamé coefficient.

Elasticity problem is a vectorial problem, is not the dimension 3? I could not understand where I making a mistake I guess I have conceptual misunderstanding at some point. Could you help me on this problem?

2.) I am not sure if this is a bug or not. When I form my matrices for the scalar problem explained above. I export them in the matrix market format using the gmm++ functions, but sometimes in the export, if the matrix dimension are high, say 13690, I get 'nan' entries in the exported matrix. I tried the hb export format, and it seems to work correctly for the same problem, I do not get any 'nan' entries in the matrices exported. If you like I can send you these files for your further experimentation.

Yes please, and if possible the smallest program producing these files.



With the kindest regards,


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