On Sun, Dec 25, 2011 at 14:02, Mark F. Adams <mark.adams at columbia.edu>wrote:
> I've looked at ksp/ksp/examples/tutorial/ex56 and the modification that I > make to emin and emax seem to be essential and very useful, respectively. > But I am seeing something funny with Cheb. > Are you comparing to "-mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.1,0,1.1" or do you mean relative to some naive Cheby configuration? > > Jed: I'm seeing very little difference in convergence rates on ex56 when > I use a first, second or fourth order Cheb smoother. I've seen some cases > where the final residual was slightly larger with a higher order smoother. > I think there is something wrong here ... > Can you show me an example? I have certainly seen it make a different for other problems. > > Also, I thought we had added something like -pc_mg_smooth to set the > number of smoothing steps when you are using the same smoother for the up > and down smoother. I can not see a command for this. I did '-help | grep > smooth', and I tried a few things. So to test this you need to manually > fix the smoothing steps at about line 662 in gamg.c. > We would normally use something like -mg_levels_ksp_max_it 3. Or are you talking about applying first-order Cheby multiple times? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20111225/0f90006d/attachment.html>