On Dec 25, 2011, at 3:07 PM, Jed Brown wrote: > 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?
I set the KSP to cheby as the default, then do a KSPGetOptions, and then if its (still) cheby I set the min and max eigenvalues manually. > > > 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. OK, well we need to think about this then. Maybe we can take a look at it at Brown in January. There must be some bad interaction in the way that I'm using it. The code is around 662 in gamg.c. > > > 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? Damn, I knew this, I forgot. Thanks, Mark -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20111226/171427a6/attachment.html>
