<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Dec 25, 2011, at 3:07 PM, Jed Brown wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="gmail_quote">On Sun, Dec 25, 2011 at 14:02, Mark F. Adams <span dir="ltr"><<a href="mailto:mark.adams@columbia.edu">mark.adams@columbia.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>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.</div></blockquote><div>
<br></div><div>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?</div></div></blockquote><div><br></div><div>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.</div><br><blockquote type="cite"><div class="gmail_quote"><div> </div><blockquote class="gmail_quote" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex; position: static; z-index: auto; ">
<div><br></div><div>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 ...</div>
</blockquote><div><br></div><div>Can you show me an example? I have certainly seen it make a different for other problems.</div></div></blockquote><div><br></div><div>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.</div><br><blockquote type="cite"><div class="gmail_quote"><div> </div><blockquote class="gmail_quote" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex; position: static; z-index: auto; ">
<div><br></div><div>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.</div>
</blockquote></div><br><div>We would normally use something like -mg_levels_ksp_max_it 3. Or are you talking about applying first-order Cheby multiple times?</div>
</blockquote></div><div><br></div>Damn, I knew this, I forgot.<div><br></div><div>Thanks,</div><div>Mark<br><div><br></div><div><br><div><br></div></div></div></body></html>