Re: [Libmesh-users] Setting size of ksp parameters

[Roy S. <roy...@ic...>]

On Thu, 15 Sep 2016, Sahai, Amal wrote:

> I have an equation system consisting of multiple Linear Implicit
> systems which I am solving using Petsc. What would be the easiest
> way to set the size of krylov subspace and the preconditioner being
> employed for a particular system? I don't want to use command line
> arguments because those get applied across systems.

Hmm... for KSP options we do call KSPSetOptionsPrefix, so you ought to
be able to use -MySystemNameksp_type cg and such.

However:

We don't have any test coverage of this in libMesh (or GRINS or FIN-S
IIRC), so unless Moose has our back I'm not sure we're doing it
properly.  It didn't seem to work for me when I gave it a quick try.

IMHO we ought to be sticking an underscore at the end of the system
name before using it as a prefix...

I don't see PCSetOptionsPrefix anywhere, and I'm not sure whether it
defaults to "" or to "whatever the KSP was set to".


If that's not working right now, we do have ways to set the most basic
options in C++ via abstract base classes, but for anything even mildly
sophisticated I think you need to cast to PetscLinearSolver, extract
the ksp() or pc() reference, and use PETSc methods on those.
---
Roy