[petsc-users] CG+GAMG convergence issues in GHEP Krylov-Schur for some MPI runs

[Mark Adams]

You can run with -info and grep on GAMG, and send this.

If you are shifting a matrix then it can/will get indefinite.  If it is
just a mass matrix then Jacobi should converge quickly - does it?

On Fri, Nov 6, 2015 at 9:35 AM, Denis Davydov <davydden at gmail.com> wrote:

>
> > On 6 Nov 2015, at 17:39, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> >  If it is a true mass matrix in the finite element sense of the word
> then it should be very well conditioned and one definitely would not use
> something like GAMG on. Jacobi + CG or maybe SSOR + CG should converge
> rapidly
>
> That I understand and absolutely agree.
> It just does not explain why GAMG would fail, especially on 4 cores and
> not on 8.
>
> Regards,
> Denis.
>
>
>
>
>
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