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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi, Matt<br>
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Thank you very much for your detailed reply.<br>
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Cheers<br>
<br>
Gao<br>
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<div style="direction: ltr;" id="divRpF776425"><font color="#000000" face="Tahoma" size="2"><b>From:</b> petsc-users-bounces@mcs.anl.gov [petsc-users-bounces@mcs.anl.gov] on behalf of Matthew Knepley [knepley@gmail.com]<br>
<b>Sent:</b> Thursday, May 03, 2012 2:56 AM<br>
<b>To:</b> PETSc users list<br>
<b>Subject:</b> Re: [petsc-users] fill matrix using dynamic load balancing code<br>
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<div class="gmail_extra">On Wed, May 2, 2012 at 7:55 PM, Gao Bin <span dir="ltr">
<<a href="mailto:bin.gao@uit.no" target="_blank">bin.gao@uit.no</a>></span> wrote:<br>
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<div style="direction:ltr; font-size:10pt; font-family:Tahoma">Hi, all<br>
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(1) I am using PETSc to perform, for instance matrix-matrix multiplication. But the numerical values of the matrix are calculated from my integral code. I guess, for matrix-matrix multiplication, it might be better to distribute the rows of matrix uniformly
on processors, right?<br>
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<div>It depends on the matrix.</div>
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<div style="direction:ltr; font-size:10pt; font-family:Tahoma">(2) If yes, I have a problem in my integral code. Since I need dynamic load balancing to calculate the matrix elements and then put them into correct places by using MatSetValues. But I have two
questions regarding MatSetValues:<br>
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(2.1) If one processor calculated a lot of elements belong to another remote processor, will this become a problem for the performance? Should I make all processors calculate as many local elements as possible?<br>
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<div>It will raise the communication cost. This, of course, must be weighed against the penalty for load imbalance in your case.</div>
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<div style="direction:ltr; font-size:10pt; font-family:Tahoma">(2.2) From the manual, I see MatSetValues only caches the values, but MatAssemblyBegin() and MatAssemblyEnd() assembles the matrix. Therefore, is there any memory limit for MatSetValues, or in other
words, will it cost a lot of memory before assembling?<br>
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<div>Yes, there is a limit to the stash space:</div>
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<div><a href="http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatStashSetInitialSize.html" target="_blank">http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Mat/MatStashSetInitialSize.html</a></div>
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<div> Matt</div>
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<div style="direction:ltr; font-size:10pt; font-family:Tahoma">Thank you in advance.<br>
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Cheers<span class="HOEnZb"><font color="#888888"><br>
<br>
Gao<br>
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-- <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>
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