[petsc-users] Reusing ML preconditioner

[John Fettig]

On Wed, Jun 29, 2011 at 11:21 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>  If you pass in SAME_PRECONDITIONER to the KSPSetOperators() it is simply impossible that it will rebuild the preconditioner. There must be another explanation as to what is going on. Are you calling anything else on the KSP?

You are right.  I was playing around with options and had set it to
SAME_NONZERO_PATTERN for the first iteration at each timestep to make
sure that would work (it does), and forgot to change it back.

When it is actually set to SAME_PRECONDITIONER and I duplicate Amat to
Pmat and pass them to KSPSetOperators() before every KSPSolve, it
definitely uses the same preconditioner (as reported by -info), but
unfortunately it reverts back to the behavior I saw previously.  The
number of iterations jumps on the second timestep.

>   Is this only happing with PCML and not with other preconditioners like PCILU?

I have only tried PCML.  Let me try PCILU and get back to you.

John