<div class="gmail_quote">On Tue, Dec 21, 2010 at 21:04, Barry Smith <span dir="ltr"><<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
This is a sign that the preconditioner is seriously messed up and should not be used in its current form. It can happen if the matrix is nearly singular and for example you use an incomplete factorization for a preconditioner that just screws up the scaling like totally. Run with -ksp_monitor_true_residual and you'll see that the solver is not really solving the problem even though it thinks it is converging fine.</blockquote>
</div><br><div>FGMRES only does right preconditioning so it should be showing the true residual.</div>