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[Getfem-users] Local re-assembly

From: Sebastien . Court
Subject: [Getfem-users] Local re-assembly
Date: Mon, 6 Jul 2015 17:03:55 +0200
User-agent: SquirrelMail/1.4.22

Dear getfem users,

I have a problem with the assembling of a matrix procedure on a selected

getfem::asm_stiffness_matrix_for_linear_elasticity(Alocal, mim_p, mf,
mf_coeff, plain_vector(mf_coeff.nb_dof(), lambdax),
plain_vector(mf_coeff.nb_dof(), mux), LOCAL);

"mim_p" is a "getfem::mesh_im_level_set" corresponding to
"INTEGRATE_OUTSIDE" or "INTEGRATE_INSIDE" for a given boundary. The idea
is to copy this matrix on the terms of an initial matrix "Ap" assembled
with a "mim" which does not see the boundary:

gmm::copy(gmm::sub_matrix(Alocal, I_local, I_local), gmm::sub_matrix(Ap,
I_local, I_local));

where I_local is a "gmm::unsorted_sub_index" object.

Then I get back the partial matrix I am interested in, corresponding to
the side of "mim_p" with the use of reduction and extension matrices (from
"mf" to a partial_mesh_fem "mf_p", and it works).

---> The problem seems to come from the definition of the region "LOCAL" I
define. When "LOCAL" contains all the convexes of the mesh, it works
perfectly, which let me think that all my other rountines work.

For being sure, when I test my code I am considering already the wanted
matrix Ap, already assembled with the mesh_mim_level_set "mim_p".

For defining "LOCAL", I select the convexes of the mesh intersected by the
boundary. It does not work, and visually the problems take place indeed
around the boundary.

1) Shall I need to consider more convexes? A priori there is no such a
reason, since at the beginning I consider the desired matrix, before
copying some partial terms (as I said, when I copy all the terms, with
LOCAL corresponding to the whole mesh, it works).

2) Is this can be due to the use of "gmm::unsorted_sub_index"?

3) Is this procedure leads to some re-numbering which could explain this?

4) Is there a problem with the function
"getfem::asm_stiffness_matrix_for_linear_elasticity" that I am not aware
of? A priori no, I have checked the definition of this function.

Thank you in advance for sharing with me some ideas in order to fix this

Best regards,

Sebastien Court

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