[petsc-users] PCFactorSetMatSolverPackage / PCFactorGetMatSolverPackage

[Hong Zhang]

Clemens,
Petsc's LDLt decomposition is likely different from mumps' LDLt.
Are you sure you want Petsc's D, but use mumps LDLt?

I suggest sending a request to mumps developer on how to accessing mumps' D.

Hong

On Tue, Aug 2, 2011 at 8:12 AM, Matthew Knepley <knepley at gmail.com> wrote:
> 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>> 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
>