[petsc-users] PCFactorSetMatSolverPackage / PCFactorGetMatSolverPackage

[Matthew Knepley]

On Tue, Aug 2, 2011 at 12:53 PM, Clemens Domanig <clemens.domanig at uibk.ac.at
> wrote:

> Maybe I should describe the hole problem.
> I'm using MUMPS to make LDLt decomposition - all from command line.
> But sometimes I need the diagonal entries (respectively the number of
> negative entries) of the D matrix. But there is no way to get this
> information back from MUMPS via petsc ( as far as I found out).


Yes, we have no access to MUMPS internal data.


> There was the suggestion to use MatGetIntertia but this is only for
> off-diagonal-information.


I am not sure what you mean by that.


> So I used
> PCSetType( prec, PCCHOLESKY);
> PCFactorGetMatrix( prec, &M);
> MatGetDiagonal( M, z);
> It only works without MUMPS and gives me the diagonal entries I want in
> Matrix M - although the entries are 1/x.
> Vector z is full of zeros - only the last entry is the 'same' as in M (x
> instead of 1/x).
>
> So the idea was to somehow turn off MUMPS if I need the diagonal entries
> and then turn it on again.
>

Here is the easiest way to do it. Keep two complete solvers

  a) KSP with MUMPS

  b) KSP with Cholesky, give this one KSPSetOptionsPrefix(ksp, "diag_");

That way -diag_pc_type cholesky will work. Then use the solver you want.


> The problem with PCFactorGetMatSolverPackage is I didn't manage to use it.
>
> const MatSolverPackage pack;
> PCFactorGetMatSolverPackage( prec, &pack);
> PetscSynchronizedPrintf( PETSC_COMM_WORLD, "%s\n", pack);
> I expected 'mumps' as output but got 'H??????tdH3%0'
>

It would seem its not yet setup.

   Matt


> Thx
>
>
>
> Matthew Knepley wrote:
>
>  On Tue, Aug 2, 2011 at 9:28 AM, Clemens Domanig <
>> clemens.domanig at uibk.ac.at <mailto:clemens.domanig at uibk.**ac.at<clemens.domanig at uibk.ac.at>>>
>> wrote:
>>
>>    Hi,
>>
>>    usually I'm using MUMPS by puting '-pc_factor_mat_solver_package
>>    mumps' into the .petscrc.
>>    Now I want to change in runtime between MUMPS and non-MUMPS so I
>>    tried to turn it on with
>>    PCFactorSetMatSolverPackage( pre, MAT_SOLVER_MUMPS);
>>    but I doesn't have any effect.
>>
>>
>> This is complicated because you have to set this at the right time during
>> the solver setup process.
>> Command line arguments are much easier. However, you should call this
>> after the preconditioner
>> type is set, but before it is setup.
>>
>>    I also have a problem with PCFactorGetMatSolverPackage(). How can I
>>    get back an output as described in the documentation that has the
>>    type 'const'?
>>
>>
>> What is the problem? I do not understand?
>>
>>    Matt
>>
>>    Thx - Clemens
>>
>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>
>


-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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