Re: [Getfem-users] Local re-assembly

[Yves Renard]

Dear Sebastien,

I do not really understand why you want to restrict the assembly to the
elements cut by the boundary.
A priori, even if you need only the information on those elements, the
neighbour elements are also contributing to the stiffness matrix you
compute.

Best regards,

Yves.




Le 06/07/2015 17:03, address@hidden a écrit :
> Dear getfem users,
>
> I have a problem with the assembling of a matrix procedure on a selected
> region:
>
> 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
> problem.
>
> Best regards,
>
> Sebastien Court
>
>
>
>
>
>
>
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-- 

  Yves Renard (address@hidden)       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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