[petsc-users] PCFactorSetMatSolverPackage / PCFactorGetMatSolverPackage

[Clemens Domanig]

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


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'
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