On Fri, Nov 25, 2011 at 15:11, Dominik Szczerba <dominik at itis.ethz.ch>wrote:
> Yes, the system is badly conditioned. But am I right with my > (experimental) finding that the ultimate way to go is -ksp_type > preonly? Will it do what I want: just solve my system exactly once > using MUMPS and not Krylov? > Direct solvers are not immune to numerical stability issues. -ksp_type preonly does not check whether the system has been solved, it just uses whatever the preconditioner (direct solve in this case) returned. Putting it inside a Krylov method generally makes it more robust. If the residual is not actually small, you should try different MUMPS flags (consult their user's manual) or try a different solver. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111125/8935bf6c/attachment.htm>
