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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Thank you Matt.
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<div><span style="font-size: 10pt;">Hui</span></div>
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<div id="divRpF778676" style="direction: ltr;"><font face="Tahoma" size="2" color="#000000"><b>From:</b> Matthew Knepley [knepley@gmail.com]<br>
<b>Sent:</b> Tuesday, February 24, 2015 2:03 AM<br>
<b>To:</b> Sun, Hui<br>
<b>Cc:</b> petsc-users@mcs.anl.gov<br>
<b>Subject:</b> Re: [petsc-users] On user defined PC of schur complement<br>
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<div class="gmail_quote">On Tue, Feb 24, 2015 at 12:08 AM, Sun, Hui <span dir="ltr">
<<a href="mailto:hus003@ucsd.edu" target="_blank">hus003@ucsd.edu</a>></span> wrote:<br>
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<div style="direction:ltr; font-family:Tahoma; color:#000000; font-size:10pt">I have a block matrix [A, B; C, D], and I want to use Schur complement to solve the linear system [A, B; C, D] * [x; y] = [c; d].
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<div>I want to apply a preconditioner for solving ( D - C*A^(-1)*B ) y = rhs. And it is easy for me to find an A' which is approximate to A, and A'^(-1) is easy to get. So for this part, I can easily define a preconditioner matrix P = <span style="font-size:10pt">(
D - C*A'^(-1)*B ) using </span><span style="font-family:Menlo; font-size:11px">PCFieldSplitSchurPrecondition</span><span style="font-size:10pt">. The next step is that I want to do incomplete LU factorization for </span><span style="font-size:10pt">P as my
left and right preconditioner for solving </span><span style="font-size:10pt">( D - C*A^(-1)*B ) y = rhs using gmres or bcgs. </span></div>
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<div><span style="font-size:10pt">My question is since part of the PC is user defined, and part of it is PETSC defined, how can I combine them? Can I do something like:</span></div>
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<p style="margin-right:0px; margin-left:0px; font-size:11px; font-family:Menlo">ierr = PCFieldSplitSchurPrecondition(pc, PC_FIELDSPLIT_SCHUR_PRE_USER, P);CHKERRQ(ierr);</p>
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<div>Once you specify the preconditioner matrix, you can use a factorization preconditioner:</div>
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<div> -fieldsplit_1_pc_type ilu</div>
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<div> Matt</div>
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<pre width="80" style="background-color:rgb(255,255,255)"><span style="font-family:Menlo; font-size:11px">ierr = PCSetType(pc, PCILU);CHKERRQ(ierr);</span></pre>
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<div><span style="font-size:10pt">Hui</span></div>
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-- <br>
<div class="gmail_signature">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>
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