Re: [Getfem-users] GMM++ Preconditioner

[Danesh Daroui]

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#preconditioners
>
> 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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-- 
Danesh Daroui
Ph.D Student
Lulea University of Technology
http://www.ltu.se

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