[petsc-users] Reusing ML preconditioner

[John Fettig]

On Wed, Jun 29, 2011 at 11:35 PM, John Fettig <john.fettig at gmail.com> wrote:
>>   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.

PCILU doesn't work at all on the second timestep in either version.
The solution hasn't met tolerances after 10000 iterations, whereas it
only took ~100 in the first timestep.  But the solutions match in both
versions.

PCHYPRE works, and the behavior is identical in both versions of my
code.  The preconditioner also loses effectiveness in the second
timestep (similar to the MatCreate*WithArrays version with ML), but at
least the behavior is consistent between versions.

The fact that ML can do so well on the second iteration is somewhat
surprising.  If it is keeping the factorization of the coarse grid, I
would think that would need to be updated.  However, shouldn't the
restriction/interpolation operators remain relatively decent if the
structure of the matrix doesn't change?

John