[petsc-users] Monotonic convergence in FGMRES.

[Jed Brown]

On Tue, Dec 21, 2010 at 21:16, Vijay S. Mahadevan <vijay.m at gmail.com> wrote:

> Jed, I ask because after the restart, the residual changes 10 orders
> of magnitude and a-priori, it is quite hard to decide the restart
> number. Yes in the test case I presented, the residual gets close
> enough to the tolerance  and I can afford few more vector storage but
> for a much refined problem, this might not be the case and so it
> worries me.
>

What happens if you run with -ksp_gmres_modifiedgramschmidt?  This is slow
in parallel, but provides insight into what is causing the problem.

My initial tests with bcgs were not satisfactory (very bad convergence
> as compared to gmres) but I tried GCR just now and it seems to
> converge correctly to the right solution, monotonically for the same
> problem.
>

GCR provides a cheap way to access the solution, see what it does with
monitor_true_residual.
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