[petsc-users] PCFactorSetUpMatSolverPackage with SNES

[David Knezevic]

On Tue, Mar 1, 2016 at 1:56 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Mar 1, 2016 at 12:52 PM, David Knezevic <
> david.knezevic at akselos.com> wrote:
>
>> Based on KSP ex52, I use PCFactorSetUpMatSolverPackage in the process of
>> setting various MUMPS ictnl options. This works fine for me when I'm
>> solving linear problems.
>>
>> I then wanted to use PCFactorSetUpMatSolverPackage with the PC from a
>> SNES object. I tried to do this with the following code (after calling
>> SNESCreate, SNESSetFunction, and SNESSetJacobian):
>>
>> KSP snes_ksp;
>> SNESGetKSP(snes, &snes_ksp);
>> PC snes_pc;
>> KSPGetPC(snes_ksp, &snes_pc);
>> PCFactorSetMatSolverPackage(snes_pc, MATSOLVERMUMPS);
>> PCFactorSetUpMatSolverPackage(snes_pc);
>>
>> However, I get a segfault on the call to PCFactorSetUpMatSolverPackage in
>> this case. I was wondering what I need to do to make this work?
>>
>> Note that I want to set the MUMPS ictnl parameters via code rather than
>> via the commandline since sometimes MUMPS fails (e.g. with error -9 due to
>> a workspace size that is too small) and I need to automatically re-run the
>> solve with different ictnl values when this happens.
>>
>
> That is a good reason. However, I would organize this differently. I would
> still set the type from the command line.
> Then later in your code, after SNES is setup correctly, you get out the PC
> and reset the icntl values if you have a
> failure. Its very difficult to get the setup logic correct, and its one of
> the most error prone parts of PETSc. RIght now,
> the most reliable way to do things is to have all the information
> available up front in options.
>
> Someday, I want to write a small DFA piece in PETSc that can encode all
> this logic so that simple errors people
> make can be diagnosed early with nice error messages.
>
>   Thanks,
>
>      Matt
>

OK, thanks for the info, I'll go with that approach.

David
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