[petsc-dev] factortype and -pc_type lu

[Matthew Knepley]

On Wed, Aug 17, 2016 at 10:15 AM, Pierre Jolivet <pierre.jolivet at enseeiht.fr
> wrote:

> Dear Hong,
> Thank you for your answer.
> I understand the error message, but I don’t understand why setting the
> preconditioner to be of type LU, i.e., factorizing the matrix, does not set
> the factortype to MAT_FACTOR_LU.
>

It sounds like you were using the wrong matrix. If the factorization is
out-of-place, then A is not the factored matrix.

   Matt


> More puzzling to me is the fact that in the output, one can see:
>
>       Factored matrix follows:
>         Mat Object: 1 MPI processes
>
> but that the error is then that the matrix is unfactored. Anyway, as you
> suggested, this works:
>   Mat F;
>   PCFactorGetMatrix(pc, &F);
>   MatSolve(F, b, x);
>
> Thank you,
> Pierre
>
> On Aug 17, 2016, at 4:34 PM, Hong <hzhang at mcs.anl.gov> wrote:
>
> Pierre:
>
>>
>> [0]PETSC ERROR: Object is in wrong state
>> [0]PETSC ERROR: Unfactored matrix
>>
>
> indicates that your input matrix is an  Unfactored matrix.
>
> If you want to replace KSPSolve() with your own MatMatSolve, you need use
> following blocks
> to replace KSPSolve() :
> Mat F;
>   ierr = KSPGetPC(ksp,&pc);
>   ierr = PCFactorSetMatSolverPackage(pc,MATSOLVERPETSC);
>   ierr = PCFactorSetUpMatSolverPackage(pc); /* call MatGetFactor() to
> create F */
>   ierr = PCFactorGetMatrix(pc,&F);
>   ierr = KSPSetUp(ksp);
>   ierr = MatSolve(F,b,x);
>
> Hong
>
>
>
>> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
>> for trouble shooting.
>> [0]PETSC ERROR: Petsc Development GIT revision: v3.7.3-1165-gfeaa1dd  GIT
>> Date: 2016-08-16 11:58:28 -0500
>>
>> Is this the expected behavior? How should I call MatSolve?
>> The rationale for calling MatSolve instead of KSPSolve (for which there
>> is obviously no error) is that I need to use MatMatSolve in my
>> application—because there is no KSPSolve(KSP, Mat, Mat), and the behavior
>> is the same for both MatSolve and MatMatSolve.
>>
>> Thank you,
>> Pierre
>
>
>
>


-- 
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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