[petsc-users] Convergence of iterative linear solver

[Matthew Knepley]

On Mon, Jun 1, 2015 at 4:06 PM, Eduardo <erocha.ssa at gmail.com> 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
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