On Sat, Nov 3, 2012 at 1:17 PM, w_ang_temp <span dir="ltr"><<a href="mailto:w_ang_temp@163.com" target="_blank">w_ang_temp@163.com</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="line-height:1.7;font-size:14px;font-family:arial"><div><span style="line-height:1.7">>At 2012-11-04 01:08:26,"Jed Brown" <</span><a href="mailto:jedbrown@mcs.anl.gov" target="_blank" style="line-height:1.7">jedbrown@mcs.anl.gov</a><span style="line-height:1.7">> wrote:</span><br>
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<p>>1. What kind of equation are you solving? AMG is not working well if it takes that many iterations.<br></p>
<p>I just deal with the typical soil-water coupled geotechnical problems. It is a typical finite element equation. The matrix is 30000X30000 and ill-conditioned.</p></blockquote></div></blockquote><div><br></div><div>We are now at the root of your problem. Solvers do not work on discretizations, they work on equations. No</div>
<div>solver is designed for "finite elements", and there is no typical finite element problem.</div><div><br></div><div>Multigrid works best on elliptic equations with smooth coefficients. Without that, you have to do special things.</div>
<div><br></div><div>I can tell from the above discussion that you have not spent a lot of time researching successful preconditioning</div><div>strategies for your problem in the literature. This is always the first step to building a high performance solver.</div>
<div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="line-height:1.7;font-size:14px;font-family:arial">
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex"><p>2.</p>
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<div><font color="#ff0000" size="4" face="courier new, monospace"><b> ##########################################################</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # WARNING!!! #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # This code was compiled with a debugging option, #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # To get timing results run ./configure #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # using --with-debugging=no, the performance will #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # be generally two or three times faster. #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> # #</b></font></div>
<div><font color="#ff0000" size="4" face="courier new, monospace"><b> ##########################################################</b></font></div></div>
<div class="gmail_extra">It is true a debugging version. And I used the same version dealing with the same problem, one preconditioner is asm<br>and the other is amg. The time with amg is about 3 times as with asm. I do not know the reason. And I also do not know the </div>
<div class="gmail_extra">meaning of '[0]PCSetData_AGG bs=1 MM=7601'.<br><br></div></blockquote></div><br><br><span title="neteasefooter"><span></span></span></blockquote></div><br><br clear="all"><div><br></div>-- <br>
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener<br>
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