<div><br></div><div>I tried to solve linear systems with PETSC.</div><div><br></div><div>There are two linear systems.</div><div>We got a solution of one of them.</div><div>For another one, the PETSC solution does not converge.</div><div><br></div><div>Thus, I out put the eigenvalues of these two coefficient matrixes (in the attachments)</div><div>in order to find if there is a difference between them.</div><div>Maybe, these eigenvalues can help me to know why that system doesn't converge.</div><div><br></div><div>However, I can not find a difference. </div><div>Do you have some suggestions about solving this non-convergence linear system?</div><div>Here is my code:</div><div><br></div><div>
<pre style="margin-top: 0px; margin-bottom: 0px;"><!--StartFragment--><span style=" color:#c0c0c0;"> </span><span style=" color:#800080;">PetscReal</span><span style=" color:#c0c0c0;"> </span>rtol=(<span style=" color:#000080;">1.e-4</span>)*pow(h,<span style=" color:#000080;">4.0</span>);</pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span><span style=" color:#800080;">PetscReal</span><span style=" color:#c0c0c0;"> </span>stol=(<span style=" color:#000080;">1.e-3</span>)*pow(h,<span style=" color:#000080;">4.0</span>);</pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><br></pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>KSPSetTolerances(ksp,<span style=" color:#c0c0c0;"> </span>rtol,<span style=" color:#c0c0c0;"> </span>stol,<span style=" color:#c0c0c0;"> </span><span style=" color:#000080;">PETSC_DEFAULT</span>,<span style=" color:#c0c0c0;"> </span><span style=" color:#000080;">PETSC_DEFAULT</span>);</pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><br></pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>KSPGetPC(ksp,<span style=" color:#c0c0c0;"> </span>&pc);</pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>PCSetType(pc,<span style=" color:#c0c0c0;"> </span><span style=" color:#000080;">PCGAMG</span>);</pre>
<pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>KSPSetFromOptions(ksp);</pre><pre style="margin-top: 0px; margin-bottom: 0px;">
<pre style="margin-top: 0px; margin-bottom: 0px;"><!--StartFragment--><span style=" color:#c0c0c0;"> </span>KSPSetUp(ksp);</pre><pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>KSPSolve(ksp,<span style=" color:#c0c0c0;"> </span>load_vect,<span style=" color:#c0c0c0;"> </span>m_solut);</pre><pre style="margin-top: 0px; margin-bottom: 0px;"><span style=" color:#c0c0c0;"> </span>KSPGetConvergedReason(ksp,<span style=" color:#c0c0c0;"> </span>&reason);</pre><pre style="margin-top: 0px; margin-bottom: 0px;"><br></pre><pre style="margin-top: 0px; margin-bottom: 0px;"><br></pre><pre style="margin-top: 0px; margin-bottom: 0px;">Thanks, </pre><pre style="margin-top: 0px; margin-bottom: 0px;"><br></pre><pre style="margin-top: 0px; margin-bottom: 0px;">Meng</pre></pre></div><div><div><br></div><div style="font-size: 12px;font-family: Arial Narrow;padding:2px 0 2px 0;">------------------ Original ------------------</div><div style="font-size: 12px;background:#efefef;padding:8px;"><div><b>From: </b> "Matthew Knepley";<knepley@gmail.com>;</div><div><b>Send time:</b> Friday, Apr 25, 2014 5:53 AM</div><div><b>To:</b> "Oo "<wumeng07maths@qq.com>; <wbr></div><div><b>Cc:</b> "petsc-users"<petsc-users@mcs.anl.gov>; <wbr></div><div><b>Subject: </b> Re: [petsc-users] Convergence_Eigenvalues_k=3</div></div><div><br></div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Apr 24, 2014 at 12:57 PM, Oo <span dir="ltr"><<a href="mailto:wumeng07maths@qq.com" target="_blank">wumeng07maths@qq.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="">
<br></div><div style="">Hi,</div><div style="">
<br></div><div style="">For analysis the convergence of linear solver, </div><div style="">
I meet a problem.</div><div style=""><br></div><div style="">
One is the list of Eigenvalues whose linear system which has a convergence solution.</div><div style="">The other is the list of Eigenvalues whose linear system whose solution does not converge (convergenceReason=-3).</div>
</div></blockquote><div><br></div><div>These are just lists of numbers. It does not tell us anything about the computation. What is the problem you are having?</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><div style="">Do you know what kind of method can be used to obtain a convergence solution for our non-convergence case?</div>
<div style=""><br></div><div style="">
Thanks,</div><div style=""><br></div><div style="">
Meng</div></div></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
</div></div></div>