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<DIV>Hello, Matthew</DIV>
<DIV> </DIV>
<DIV> I just mean that the problem that I am resolving is a finite element problem. The linear system of it is true elliptic equations.</DIV>
<DIV>I heared that AMG was an efficient solver, so I just want to have a try about AMG and find that if it is efficient. </DIV>
<DIV> By the way, I want to confirm a conception. In my view, AMG itself can be a solver like gmres. It can also be used as a preconditioner </DIV>
<DIV>like jacobi and is used by combining with other solver. Is it right? If it is right, how use AMG solver?</DIV>
<DIV> </DIV>
<DIV> Thanks.</DIV>
<DIV> </DIV>
<DIV> Jim<BR><BR></DIV>
<DIV></DIV>
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<DIV><BR></DIV>>ÔÚ 2012-11-04 01:21:59£¬"Matthew Knepley" <<A href="mailto:knepley@gmail.com">knepley@gmail.com</A>> дµÀ£º<BR>
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" id="isReplyContent">><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>
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<DIV><SPAN style="LINE-HEIGHT: 1.7">>At 2012-11-04 01:08:26,"Jed Brown" <</SPAN><A style="LINE-HEIGHT: 1.7" href="mailto:jedbrown@mcs.anl.gov" target="_blank">jedbrown@mcs.anl.gov</A><SPAN style="LINE-HEIGHT: 1.7">> wrote:</SPAN><BR></DIV>
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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>
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<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>
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<DIV>>Multigrid works best on elliptic equations with smooth coefficients. Without that, you have to do special things.</DIV>
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<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>
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<DIV> > Thanks,</DIV>
<DIV><BR></DIV>
<DIV>> Matt</DIV>
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<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></DIV></BLOCKQUOTE></DIV></div><br><br><span title="neteasefooter"><span id="netease_mail_footer"></span></span>