Re: [Getfem-users] QUterm vs. parallelization

[Yves Renard]

Dear Igor,

Unfortunately, the parrallelization of Getfem is still incomplete. You are 
right, th brick mdbrick_QU_term is not parallelized. In fact, the 
modification to parallelize it is not difficult. You have to replace the last 
argument of asm_qu_term, which is boundary, by the term
mf_u.linked_mesh().get_mpi_sub_region(boundary)
in the definition of the brick (getfem_modeling.h).
The effect is that the assembly will be done in a distributed way with respect 
to a partition of the mesh done with metis.

In fact, all model brick have to be modified in that way to be used in a 
parallel version.

I commit this change in the gna repository.

Best regards,

Yves.


On Friday 03 April 2009 11:29, Igor Peterlik wrote:
> Dear GetFEM team,
>
> I would like to ask about a bit strange behavior of the QUterm brick
> being used with GETFEM_PARA_LEVEL=2.
> First, I noticed that my application composed of the Helmholtz,
> Dirichlet (twice) and QUterm bricks gives
> different results in sequential and parallel version (and moreover the
> result in parallel version depends on the number of
> the processors). I found out that the QUterm brick modifies the entire
> system matrix on each process. Maybe I had missed
> something but it seemed to me that this was not correct behavior
> (maybe QUterm is not compatible with paralel mode...).
> As a workaround, I added a condition to the gmm:add  as shown below:
>
> if (getfem::MPI_IS_MASTER())
>      gmm::add(get_K(), gmm::sub_matrix(MS.tangent_matrix(), SUBI));
>
> in the  mdbrick_QU_term::do_compute_tangent_matrix().
> so the system matrix is modified only once. It seems this helped,
> since the solution is now invariant wrt. the number
> of CPUs. Nevertheless, this is not the real solution I guess.
>
> BTW is there some (at least) small documentation concerning the
> paralelization (which parts are parallelized and how)?
>
>               Regards
>
>                                Igor
>
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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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