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 <[email protected]> wrote: > > > On 6 Nov 2015, at 17:39, Barry Smith <[email protected]> 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. > > > > >
