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<div class="">Thanks a lot, Matt. </div>
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<div class=""> 1) Are you using DMStag? If so, the field split might be able to be automated.</div>
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I think this is true only if I have one component on each vertex/face/edge. I have two dofs on vertex, corresponding to component 0 and 1. They are mixed together as I understand. </div>
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<div class="">Meanwhile, I am testing the three field version using automated split and two nested fieldsplit (so pc will handle vertex dofs together). I expect it will work. </div>
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<div class=""> 2) Checking the division:</div>
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<div class="">I am trying to do </div>
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<div class=""> Schur complement {1, 2, 3} and {0}</div>
<div class=""> Multiplicative {1} and {2, 3}</div>
<div class=""> Schur complement {2} and {3}</div>
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<div class="">The first level is a saddle point problem and the last level is parabolization. I know the diagonal operator for {1} and Schur complement for {3} works well with amg.</div>
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<div class="">Qi</div>
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<div class="">On Mar 12, 2022, at 3:21 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div>
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<div dir="ltr" class="">On Fri, Mar 11, 2022 at 3:32 PM Tang, Qi <<a href="mailto:tangqi@msu.edu" class="">tangqi@msu.edu</a>> wrote:<br class="">
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Hi,<br class="">
I am trying to solve a four field system with three nested fieldsplit (I am in petsc/dmstag directly). I think I have all the IS info in the original system. I am wondering how to set up IS for the split system.<br class="">
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<div class="">Some questions first:</div>
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<div class=""> 1) Are you using DMStag? If so, the field split might be able to be automated.</div>
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<div class=""> 2) Checking the division:</div>
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<div class=""> Schur complement {1, 2, 3} and {0}</div>
<div class=""> Multiplicative {1,2} and {3}</div>
<div class=""> Schur complement {1} and {2}</div>
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<div class=""> Thanks,</div>
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<div class=""> Matt</div>
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More specifically, I would like to call something like this<br class="">
-pc_type fieldsplit -pc_fieldsplit_type schur -pc_fieldsplit_0_fields 0 -pc_fieldsplit_1_fields 1,2,3<br class="">
-fieldsplit_1_ksp_type fgmres -fieldsplit_1_pc_type fieldsplit -fieldsplit_1_pc_fieldsplit_type multiplicative<br class="">
-fieldsplit_1_fieldsplit_1_ksp_type fgmres -fieldsplit_1_fieldsplit_1_pc_type fieldsplit -fieldsplit_1_fieldsplit_1_pc_fieldsplit_type schur<br class="">
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I know the first level probably would work. But the second and third levels would not.<span class="Apple-converted-space"> </span><br class="">
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We have two components living on one type of dofs. So the natural split 0,1,2,3 do not work. Therefore, at the first level I am setting up split through<br class="">
PCFieldSplitSetIS(pc, “i", myis[i]);<br class="">
How could I know the sub ISs and set it up correctly? Thanks.<br class="">
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Qi Tang<br class="">
T5@LANL<br class="">
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--<span class="Apple-converted-space"> </span><br class="">
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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!mFfBXSXv1xb00aJzISaY9ymPjPF_fX30APRsXjauIJzSwgpBxk1pdgI22I9PEg$" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a></div>
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