[petsc-users] GAMG PC dependence on right-hand side

Jed Brown jedbrown at mcs.anl.gov
Thu Jul 11 13:00:51 CDT 2013

John Mousel <john.mousel at gmail.com> writes:

> I'm trying to reuse the PC constructed by GAMG during a sub-iterative
> procedure where KSPSolve is called with the same matrix repeatedly. The
> right-hand side changes during the sub-iteration. I've been attempting to
> use SAME_PRECONDITIONER for nit = 2..., 

What do you mean by SAME_PRECONDITIONER?  If you are solving with the
same matrix, you can just call KSPSolve without KSPSetOperators.

> Is there a dependence on the right-hand side in GAMG somewhere?

It uses a pseudo-random number generator for eigenvalue estimation.  Try

  -random_seed 1

to your run and see if it cuts the variation you see.
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