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<div class="">Thanks a lot, Patrick. We appreciate your help.</div>
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<div class="">On Apr 18, 2021, at 11:30 PM, Patrick Sanan <<a href="mailto:patrick.sanan@gmail.com" class="">patrick.sanan@gmail.com</a>> wrote:</div>
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We have this functionality in a branch, which I'm working on cleaning up to get to master. It doesn't use PETScSection. Sorry about the delay!<br class="">
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<div class="">You can only use PCFieldSplitSetDetectSaddlePoint when your diagonal entries being zero or non-zero defines the splits correctly. </div>
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<div class="">Am 17.04.2021 um 21:09 schrieb Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>>:</div>
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<div dir="ltr" class="">On Fri, Apr 16, 2021 at 8:39 PM Jorti, Zakariae via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" class="">petsc-users@mcs.anl.gov</a>> wrote:<br class="">
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<p class="">Hello,</p>
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<p class="">I have a DMStag grid with one dof on each edge and face center. </p>
<p class="">I want to use a PCFieldSplit preconditioner on a Jacobian matrix that I assume is already split but I am not sure how to determine the fields. </p>
<p class="">In the DMStag examples (ex2.c and ex3.c), the function PCFieldSplitSetDetectSaddlePoint is used to <font size="3" class="">determine those </font><font size="3" class="">fields based on zero diagonal entries. In my case, I have a Jacobian matrix
that does not have </font>zero<font size="3" class=""> diagonal entries. </font></p>
<p class=""><font size="3" class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">Can I use that </span></font><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">PCFieldSplitSetDetectSaddlePoint
in this case? </span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">If not, how should I do? </span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">Should</span><font size="3" class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class=""> I do like this example (</span></font><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class=""><a href="https://urldefense.com/v3/__https://www.mcs.anl.gov/petsc/petsc-master/src/ksp/ksp/tutorials/ex43.c.html__;!!HXCxUKc!jbBwV2h9luOW4dtBcNh6n_W1ULQnSVeXpxl0Ef1752s4Hlef-nC2JcnksFSO3Q$" target="_blank" class="">https://www.mcs.anl.gov/petsc/petsc-master/src/ksp/ksp/tutorials/ex43.c.html</a>)</span><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">: </span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">const PetscInt Bfields[1] = {0},Efields[1] = {1};</span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">KSPGetPC(ksp,&pc);</span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">PCFieldSplitSetBlockSize(pc,2);</span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">PCFieldSplitSetFields(pc,"B",1,Bfields,Bfields); PCFieldSplitSetFields(pc,"E",1,Efields,Efields); </span></p>
<p class=""><span style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;" class="">where my B unknowns are defined on face centers and E unknowns are defined on edge centers?</span></p>
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<div class="">That will not work.That interface only works for colocated fields that you get from DMDA.<br class="">
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<div class="">Patrick, does DMSTAG use PetscSection? Then the field split would be automatically calculated. If not, does it maintain the</div>
<div class="">field division so that it could be given to PCFIELDSPLIT as ISes?</div>
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<div class=""> Thanks,</div>
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<div class=""> Matt</div>
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<p class="">One last thing, I do not know which field comes first. Is it the one defined for face dofs or edge dofs.</p>
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<p class="">Thank you.</p>
<p class="">Best regards,</p>
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<p class="">Zakariae</p>
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<div class="">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">
-- Norbert Wiener</div>
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<div class=""><a href="https://urldefense.com/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!HXCxUKc!jbBwV2h9luOW4dtBcNh6n_W1ULQnSVeXpxl0Ef1752s4Hlef-nC2JcmGgSwfag$" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a></div>
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