<div style="line-height:1.7;color:#000000;font-size:14px;font-family:arial"><DIV>Thanks. I will have a try.</DIV>
<DIV> </DIV>
<DIV> Jim<BR><BR><BR><BR><BR></DIV>
<DIV></DIV>
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<DIV><BR></DIV>ÔÚ 2012-10-28 21:46:23£¬"Matthew Knepley" <knepley@gmail.com> дµÀ£º<BR>
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" id="isReplyContent">On Sun, Oct 28, 2012 at 9:38 AM, 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>Hello, Jed</DIV>
<DIV> Thanks for your timely reply. I deal with the soil-water coupled problem in geotechnical engineering, </DIV>
<DIV>whose stiffness matrix is ill-conditioned. I have did some work about it, mainly finding the effective</DIV>
<DIV>solvers and preconditioners. I used the command line option like this:</DIV>
<DIV>mpiexec -n 4 ./ex4f -ksp_type cgs -pc_type sor -ksp_rtol 1.0e-15 -ksp_converged_reason.</DIV></DIV></BLOCKQUOTE>
<DIV><BR></DIV>
<DIV>If SOR works as a preconditioner, then definitely use AMG as Jed suggested. It is almost certain to work.</DIV>
<DIV><BR></DIV>
<DIV> Matt</DIV>
<DIV> </DIV>
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<DIV> So, I also want to use the multigrid just like the simple command. There is only a little introduction</DIV>
<DIV>about multigrid in the manual. Multigrid is complex and not a easy thing for me, so I just need to konw how</DIV>
<DIV>to use it simply in PETSc to solve the Ax=b system.</DIV>
<DIV> Thanks.</DIV>
<DIV> Jim<BR><BR><BR><BR><BR></DIV>
<DIV></DIV>
<DIV></DIV>
<DIV><BR></DIV>>At 2012-10-28 21:17:00,"Jed Brown" <<A href="mailto:jedbrown@mcs.anl.gov" target="_blank">jedbrown@mcs.anl.gov</A>> wrote:<BR>
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex">
<P>>Algebraic multigrid can be used directly, -pc_type gamg -pc_gamg_agg_nsmooths 1. Geometric either required that you use the PCMG interface to set >interpolation (and provide a coarse operator for non-Galerkin) or use a DM that provides coarsening capability.</P>
<P>>What kind of problem are you solving?</P>
<DIV class="gmail_quote">>>On Oct 28, 2012 6:09 AM, "w_ang_temp" <<A href="mailto:w_ang_temp@163.com" target="_blank">w_ang_temp@163.com</A>> wrote:<BR type="attribution">
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<DIV>>>Hello,</DIV>
<DIV>>> I want to use the multigrid as a preconditioner. The introduction about it in the manual is little.</DIV>
<DIV>>>So are there some typical examples or details about multigrid? Is it used just like other preconditioners</DIV>
<DIV>>>like jacobi, sor, which can be simply used in the cammand line options?</DIV>
<DIV>>> Thanks.</DIV>
<DIV>>> Jim</DIV></DIV><BR><BR><SPAN title="neteasefooter"><SPAN></SPAN></SPAN></BLOCKQUOTE></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></BLOCKQUOTE></div><br><br><span title="neteasefooter"><span id="netease_mail_footer"></span></span>