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

[Denis Davydov]

> 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.