On Tue, Dec 21, 2010 at 21:16, Vijay S. Mahadevan <[email protected]> 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.