<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I use:<div><br></div><div><div>run:</div><div> -@${MPIEXEC} -n 1 ./ex56 -ne 49 -pc_gamg_verbose -alpha 1.e-3 -ksp_monitor -ksp_type cg -pc_gamg_type sa -ksp_rtol 1.e-10</div><div><br></div><div>plus -mg_levels_ksp_max_it to adjust smoothing. </div><div><br></div><div>src/ksp/ksp/examples/tutorials has ex54 ex55 and ex56 that do a 2D scalar Lapacian, 2D elasticity and 3D elasticity respectively.</div><div><br></div><div> -ne is the number of elements on a side so for the 2D problems '-ne 100' is decent and for 3D '-ne 49' is pretty big unless you are running in parallel.</div><div><br></div><div>I've just started using -ksp_rtol 1.e-10 and retested all of these test and am seeing a very slight improvement going from 1 to 4. I would expect to see a significant drop, say 25%, in the number of iterations going from 1 to 2. The < 5% that I am seeing seems too low but I'm not 100% sure -- maybe there is nothing wrong ...</div><div><br></div><div>Mark</div><div><br></div><div><div>On Dec 26, 2011, at 10:41 AM, Jed Brown wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="gmail_quote">On Mon, Dec 26, 2011 at 00:07, 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 class="im"><blockquote type="cite"><div class="gmail_quote"><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><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>
</blockquote></div><br><div>Can you tell me how to run an example that shows this behavior?</div>
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