[petsc-users] How to access the KSP objects from a PCFIELDSPLIT Schur preconditioner

[Matthew Knepley]

On Wed, Oct 24, 2012 at 3:23 PM, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> I want to play around with some special type of a Schur complement
> preconditioner. It perfectly fits into PETSc's fieldsplit preconditioner
> (schur - full factorization). But for the inner solvers, I would like to
> create some MatShells. So I need to access both KSP objects, for the upper
> block (KSP(A_00)) and for the Schur complement (KSP(S)). How can I get
> these objects in my source code?
>

First you have to make them different. This happens when you give options
for

  -fieldsplit_1_upper_*
  -fieldsplit_1_inner_*

This is how I customize the solvers to get things like SIMPLE. Once they
are created, you
can get them by pulling apart the FS. The upper is fs->kspupper, and the
inner is the KSP
from the MATSCHUR from fs->schur.

   Matt


> Best regards,
>
> Thomas
>



-- 
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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