<div style="line-height:1.7;color:#000000;font-size:14px;font-family:arial"><DIV>Hello, Jed</DIV>
<DIV> I use the command:</DIV>
<DIV> mpiexec -n 4 ./ex4f -ksp_type cgs -pc_type gamg -pc_gamg_agg_nsmooths 1 -ksp_rtol 1.0e-15 -ksp_converged_reason</DIV>
<DIV> The error is as follows:<BR>[0]PETSC ERROR: --------------------- Error Message ------------------------------------<BR>[0]PETSC ERROR: Unknown type. Check for miss-spelling or missing external package needed for type<BR> seehttp://www.mcs.anl.gov/petsc/petsc-as/documentation/installation.html#external!<BR>[0]PETSC ERROR: Unable to find requested PC type gamg!<BR>[0]PETSC ERROR: ------------------------------------------------------------------------<BR>[0]PETSC ERROR: Petsc Release Version 3.2.0, Patch 7, Thu Mar 15 09:30:51 CDT 2012 <BR>[0]PETSC ERROR: See docs/changes/index.html for recent updates.<BR>[0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.<BR>[0]PETSC ERROR: See docs/index.html for manual pages.<BR>[0]PETSC ERROR: ------------------------------------------------------------------------<BR>[0]PETSC ERROR: ./ex4f on a arch-linu named ubuntu by geo Mon Oct 29 05:40:13 2012<BR>[0]PETSC ERROR: Libraries linked from /home
/geo/soft/petsc/petsc-3.2-p7/arch-linux2-c-opt/lib<BR>[0]PETSC ERROR: Configure run at Mon Jul 2 20:33:17 2012<BR>[0]PETSC ERROR: Configure options --with-mpi-dir=/home/geo/soft/mpich2 --download-f-blas-lapack=1 --with-x=1 --with-debugging=0 --download-parmetis --download-mumps --download-scalapack --download-blacs<BR>[0]PETSC ERROR: ------------------------------------------------------------------------<BR>[0]PETSC ERROR: PCSetType() line 67 in src/ksp/pc/interface/pcset.c<BR>[0]PETSC ERROR: PCSetFromOptions() line 184 in src/ksp/pc/interface/pcset.c<BR>[0]PETSC ERROR: KSPSetFromOptions() line 286 in src/ksp/ksp/interface/itcl.c</DIV>
<DIV> When I use 'mpiexec -n 4 ./ex4f -ksp_type cgs -pc_type sor -ksp_rtol 1.0e-15 -ksp_converged_reason', it is ok. So</DIV>
<DIV>what is the possible reason?</DIV>
<DIV> Thanks.</DIV>
<DIV> Jim<BR><BR><BR><BR><BR></DIV>
<DIV></DIV>
<DIV id="divNeteaseMailCard"></DIV>
<DIV><BR></DIV>At 2012-10-28 22:25:31,"Jed Brown" <jedbrown@mcs.anl.gov> wrote:<BR>
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" id="isReplyContent">
<P>Try the simple option I just sent.</P>
<DIV class="gmail_quote">On Oct 28, 2012 6:38 AM, "w_ang_temp" <<A href="mailto:w_ang_temp@163.com">w_ang_temp@163.com</A>> wrote:<BR type="attribution">
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">
<DIV style="LINE-HEIGHT: 1.7; FONT-FAMILY: arial; FONT-SIZE: 14px">
<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> 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">
<BLOCKQUOTE style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">
<DIV style="LINE-HEIGHT: 1.7; FONT-FAMILY: arial; FONT-SIZE: 14px">
<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></BLOCKQUOTE></div><br><br><span title="neteasefooter"><span id="netease_mail_footer"></span></span>