On Mon, Jun 1, 2015 at 4:06 PM, Eduardo <[email protected]> wrote:
> I am solving a linear system for which the preconditioned residual
> decreases, but the true residual increases (or have an erratic behavior).
> According to Petsc FAQ, this is due to a preconditioner that is singular or
> close to singular. What can I do in this case? I used GMRES with ILU
> preconditioner.
>
ILU can be spectacularly bad. We recommend switching to a preconditioner
tailored to your problem. The best
way to find these is to look in the literature.
Thanks,
Matt
> Incidentally, I tried to solve a smaller system with a direct solver
> (superlu_dist) and it ran, so the system apparently is not singular.
>
> Thanks in advance,
> Eduardo
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
