[petsc-users] About the "PetscOptionsSetValue" usage

[Filippo Spiga]

Interesting. This

KSPSetOptionsPrefix(ksp,"a_");
PetscOptionsSetValue("a_A", "1");
PetscOptionsSetValue("a_B", "2");
PetscOptionsSetValue("a_C", "3");
ierr = KSPSolve();

SNESSetOptionsPrefix(snes,"b_");
PetscOptionsSetValue("b_A", "10");
PetscOptionsSetValue("b_B", "20");
ierr = SNESSolve();

should work because the preset will be
- KSP : {A=1, B=2, C=3}
- SNES : {A=10, B=20, C=PETSC_DEFAULT}.
exactly as I want.

I know that it is possible to use API to set parameters (KSPSetType,
SNESSetType). But a lot of options of HYPRE or SUPERLU for example have no
API. Instead of mix option from command-line and API I would like to put
everything in a config file, read it and use PetscOptionsSetValue in the
right way. It seems reasonable to me.

Anyway, every suggestion is welcome (-:

Thanks a lot!

--
Filippo SPIGA, MSc Computer Science
~ homepage: http://tinyurl.com/fspiga ~

«Nobody will drive us out of Cantor's paradise.»
    -- David Hilbert

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On Fri, Dec 10, 2010 at 1:46 PM, Jed Brown <jed at 59a2.org> wrote:

> On Fri, Dec 10, 2010 at 19:22, Filippo Spiga <
> filippo.spiga at disco.unimib.it> wrote:
>
>> So SNES runs with C=3 that is different from the default. But I would like
>> to use the default because C=3 produces wrong errors. How I can easily reset
>> the options' database?
>
>
> You're making this much more complicated than necessary.  Call
>
> KSPSetOptionsPrefix(ksp,"a_");
> SNESSetOptionsPrefix(snes,"b_");
>
> KSPSetFromOptions(ksp);
> SNESSetFromOptions(snes);
>
> KSPSolve(ksp,...);
> SNESSolve(snes,...);
>
>
> Then you run the program with
>
>   -a_ksp_type gmres -a_pc_type asm -b_snes_monitor -b_ksp_type ibcgs
> -b_pc_type bjacobi
>
> or whatever.  You can control all the details of each solver independently.
>
> If you *need* to control the solvers in code (usually only if you have an
> adaptive method where *your program* takes *active* control of the solution
> process), you should pull out the objects and use the API instead of strings
> to get what you need:
>
> SNESGetKSP(snes,&inner_ksp);
> KSPSetType(inner_ksp,KSPIBCGS);
>
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