Re: [Getfem-users] GMM++ Preconditioner

[Yves Renard]

Dear Danesh

If your matrix is nearly dense (if I understand well, in your case, you have 
more than 30% of nonzero components) the dense format is the better because 
the linear algebra operations are far more optimized for dense matrices (using 
blas) than for sparse matrices.

Yves.


On dimanche 12 septembre 2010, Danesh Daroui wrote:
> Dear Renard,
> 
> Thanks for your answer. Yes you are right. In principle, using iterative
> solvers for a dense matrix is not a good idea. Maybe for special cases,
> but not in general. Please correct me if I am wrong. The reason that I
> am using a dense matrix type is that I am using a very large matrix
> where I fill each quarter separately. Two of quarters are dense and the
> others are very sparse. It is also possible to make the dense quarters
> more sparse that I am working on it. For this purpose I thought maybe it
> is better to use a dense matrix, however I leave mane zero cells in the
> memory. Do you have any suggestion? Is it possible to reference each
> quarter using a sparse format matrix like dense format in GMM++?
> 
> Regards,
> 
> D.
> 
> On 2010-09-12 17:09, Renard Yves wrote:
> > Dear Danesh,
> > 
> > The template argument for the preconditionner is the matrix type. So
> > you should declare
> > 
> > gmm::dense_matrix<double> A(100, 100);
> > 
> > filling the matrix
> > 
> > gmm::ilu_precond<gmm::dense_matrix<double> > P1(A);
> > 
> > 
> > 
> > Of course, this is not very satisfactory because an incomplete LU
> > decomposition on a dense matrix is a complete LU decomposition. You
> > should work with sparse matrices instead.
> > 
> > You can see on the following page of the documentation how to declare
> > each preconditionner :
> > 
> > http://download.gna.org/getfem/html/homepage/gmm/iter.html#preconditioner
> > s
> > 
> > Yves.
> > 
> > Danesh Daroui <address@hidden> a écrit :
> >> Dear all,
> >> 
> >> I would like to use GMM++ iterative solvers. The problem is that I can
> >> not use for example incomplete LU factorization preconditioner. Let say
> >> that I have the equation Ax=b. The I define the preconditioner as:
> >> 
> >> gmm::dense_matrix<double> A(100, 100);
> >> 
> >> // filling the matrix
> >> 
> >> gmm::ilu_precond<double> P1(A);
> >> 
> >> but I get compilation errors. It just compiled successfullt when I
> >> define:
> >> 
> >> gmm::ilu_precond<double> P1;
> >> 
> >> but there is no hint and neither sample code to show which function
> >> should I call to create the preconditioner.
> >> 
> >> Can anybody help?
> >> 
> >> Regards,
> >> 
> >> D.
> >> 
> >> 
> >> 
> >> 
> >> 
> >> _______________________________________________
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> > 
> > _______________________________________________
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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
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