Dear Jed, Sorry for late reply. This email box gets piled up... :-) I agree that solves are faster than factorization and GMRES use more MatVecMult, even with exact preconditioner. So I guess PREONLY is meaning direct solve without forming any sub-space and just one forward and backward substitutions?
Thanks, Yan On Wed, Apr 6, 2011 at 1:43 AM, Jed Brown <jed at 59a2.org> wrote: > On Wed, Apr 6, 2011 at 05:27, Matthew Knepley <knepley at gmail.com> wrote: > >> There should be no difference since direct solves take so long. > > > That is, solves are very fast compared to factorization. > > If you just want to check the residual, Richardson is cheaper than GMRES > because it will require one fewer preconditioner/matrix applications. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110407/778fdc8b/attachment.htm>
