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Matt,</div>
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At a local section point (including ghost point), how to find all the owners? For example, proc[0] and proc[2] share p. How proc[0] find that proc[2] is an owner? Any routine would provide this info?</div>
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Hong</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Matthew Knepley <knepley@gmail.com><br>
<b>Sent:</b> Wednesday, November 18, 2020 1:56 PM<br>
<b>To:</b> Lawrence Mitchell <wence@gmx.li><br>
<b>Cc:</b> Zhang, Hong <hzhang@mcs.anl.gov>; petsc-dev <petsc-dev@mcs.anl.gov><br>
<b>Subject:</b> Re: [petsc-dev] Can I call PetscSectionAddDof(s, p, ndof) at a shred 'p' by more than one processors?</font>
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<div dir="ltr">On Wed, Nov 18, 2020 at 2:19 PM Lawrence Mitchell <<a href="mailto:wence@gmx.li">wence@gmx.li</a>> wrote:<br>
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> On 18 Nov 2020, at 15:26, Zhang, Hong via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov" target="_blank">petsc-dev@mcs.anl.gov</a>> wrote:<br>
> <br>
> Matt or Jed,<br>
> Can I call PetscSectionAddDof(s,p,ndof) at a shred 'p' by more than one processors? For example,<br>
> if (rank == 0) {<br>
> PetscSectionAddDof(s,p,1) ;<br>
> } else if (rank == 1) {<br>
> PetscSectionAddDof(s,p,2) ;<br>
> } <br>
> Then, at shared 'p', section 's' has dof=3?<br>
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Sections are "local" objects that are tied together by an SF that describes point ownership.<br>
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So I think that the only thing you need is that if two processes set a dof on what is globally the same point, they should agree on how many dofs live there.<br>
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I wonder if PetscSectionAddDof (etc...) should be marked as logically collective.<br>
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<div>Right now, what you want is handled by creating a global Section from a local Section:</div>
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<div> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PetscSection/PetscSectionCreateGlobalSection.html">https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PetscSection/PetscSectionCreateGlobalSection.html</a></div>
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<div>The global Section contains global offsets for all local points, and the ghost points have negative offsets.</div>
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<div>There is no facility for combining dofs. The idea is that you know the number of dofs on each local point. If you change that</div>
<div>interpretation, you could easily use SF to add them up and broadcast the sum.</div>
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<div> Thanks,</div>
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<div> Matt</div>
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Lawrence</blockquote>
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<div>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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<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><br>
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