On Thu, May 24, 2012 at 10:19 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > I think I've fixed PCPre/PostSolve_Eisenstat() to work properly with > kspest but seems to be with ex19 a much worse smoother than SOR (both with > Cheby). I'm not sure why. With SOR we are essentially doing a few Chebyshev > iterations with > (U+D)^-1 (L+D)^-1 A x = b while with Eisenstat it is (L+D)^-1 A (U + > D)^-1 y = (L+D)^-1 b. Well no time to think about it now. > > Mark, > > Has anyone looked at using Cheby Eisentat smoothing as opposed to > Cheby SOR smoothing? > Aren't they supposed to be the same? > > Barry > > On May 24, 2012, at 1:20 PM, Jed Brown wrote: > > > On Wed, May 23, 2012 at 2:52 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > > On Wed, May 23, 2012 at 2:26 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > > > Note that you could use -pc_type eisenstat perhaps in this case > instead. Might save lots of flops? I've often wondered about doing Mark's > favorite chebyshev smoother with Eisenstat, seems like it should be a good > match. > > > > [0]PETSC ERROR: --------------------- Error Message > ------------------------------------ > > [0]PETSC ERROR: No support for this operation for this object type! > > [0]PETSC ERROR: Cannot have different mat and pmat! > > > > Also, I'm having trouble getting Eisenstat to be more than very > marginally faster than SOR. > > > > > > I think we should later be getting the eigenvalue estimate by applying > the preconditioned operator to a few random vectors, then orthogonalizing. > The basic algorithm is to generate a random matrix X (say 5 or 10 columns), > compute > > > > Y = (P^{-1} A)^q X > > > > where q is 1 or 2 or 3, then compute > > > > Q R = Y > > > > and compute the largest singular value of the small matrix R. The > orthogonalization can be done in one reduction and all the MatMults can be > done together. Whenever we manage to implement a MatMMult and PCMApply or > whatever (names inspired by VecMDot), this will provide a very low > communication way to get the eigenvalue estimates. > > > > > > I want to turn off norms in Chebyshev by default (they are very > wasteful), but how should I make -mg_levels_ksp_monitor turn them back on? > I'm already tired of typing -mg_levels_ksp_norm_type unpreconditioned. > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20120524/46b829e3/attachment.html>