[petsc-users] About the "PetscOptionsSetValue" usage

[Filippo Spiga]

(sorry in advance for the cross-posting)

Dear all,
    I recently decided to use in my program the
routine "PetscOptionsSetValue" to allow to change at runtime the parameter
of KSP/SNES. Of course, my code performs several operations on different KSP
and SNES objects. Every object should have its own set of options (different
tollerancies, different preconditioner) and I want to tune it at runtime. So
"PetscOptionsSetValue" it is great. But I have a question: when I set an
option, this option is still valid for all the program.

Let's assume this situation (it is an example, I use fake options):

PetscOptionsSetValue("A", "1");
PetscOptionsSetValue("B", "2");
PetscOptionsSetValue("C", "3");

ierr = KSPSolve();

PetscOptionsSetValue("A", "10");
PetscOptionsSetValue("B", "20");

ierr = SNESSolve();


This is what happens (if I correcly understood):
- KSP runs with this presets {A=1, B=2, C=3} that are different than
the defaults.
- SNES runs with this presets {A=10, B=20, C=3}.
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?

Thanks in advance,
Cheers

--
Filippo SPIGA, MSc Computer Science

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

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