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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>The default solver is GMRES, which can solve indefinite systems.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:#1F497D'>================================<br>
Keita Teranishi<br>
Scientific Library Group<br>
Cray, Inc.<br>
keita@cray.com<br>
================================</span><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
petsc-dev-bounces@mcs.anl.gov [mailto:petsc-dev-bounces@mcs.anl.gov] <b>On
Behalf Of </b>Anush Krishnan<br>
<b>Sent:</b> Thursday, August 26, 2010 12:08 PM<br>
<b>To:</b> petsc-dev@mcs.anl.gov<br>
<b>Subject:</b> Re: [petsc-dev] Problem with conjugate gradient solver<o:p></o:p></span></p>
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<p class=MsoNormal>Message: 2<br>
Date: Tue, 24 Aug 2010 10:56:53 -0500<br>
From: Barry Smith <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>><br>
Subject: Re: [petsc-dev] Problem with conjugate gradient solver<br>
To: For users of the development version of PETSc<br>
<<a href="mailto:petsc-dev@mcs.anl.gov">petsc-dev@mcs.anl.gov</a>>,
Victor Eijkhout <<a
href="mailto:eijkhout@tacc.utexas.edu">eijkhout@tacc.utexas.edu</a>><br>
Message-ID: <<a
href="mailto:A4C6A1ED-CDE7-4653-8046-C2797AD5AF31@mcs.anl.gov">A4C6A1ED-CDE7-4653-8046-C2797AD5AF31@mcs.anl.gov</a>><br>
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<br>
<br>
Well you are doing nothing wrong. When I run the code I get the same
results as you. I dump the matrix into Matlab and it has a negative eigenvalue
so the example is wrong. The code is handling it correctly.<br>
<br>
>> eig(full(Mat_0))<br>
<br>
ans =<br>
<br>
-0.8042<br>
0.1716<br>
0.6489<br>
1.0000<br>
1.0000<br>
1.0000<br>
1.0000<o:p></o:p></p>
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<p class=MsoNormal><br>
So are you saying that trying to solve the system of equations in the example
will always result in divergence? I tried the same program with a different
system that I know has a solution, and even that diverges. I get a proper
solution if I use the default KSP solver.<br>
<br>
Anush<br>
<o:p></o:p></p>
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<p class=MsoNormal><br>
I am cc:iing Victor who supposedly wrote the original example. <o:p></o:p></p>
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<p class=MsoNormal><br>
Barry<br>
<br>
Attached is the matrix saved with -mat_view_matlab<o:p></o:p></p>
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