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Hi Miguel,</div>
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I believe what you may be looking for is DMSwarmGetCellSwarm which extracts the fields from the swarm for a specified cell</div>
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<a href="https://urldefense.us/v3/__https://petsc.org/release/manualpages/DMSwarm/DMSwarmGetCellSwarm/__;!!G_uCfscf7eWS!ZNzXAukaJWoy9gfF0ZpkipSh7IvFVWu9UsybjhiA8z5_GHxWHwJ60oFlfUGwwh73aGqUO3XB4W8Mo4B5m7I4YoqhM1c$" id="LPlnk824560">https://petsc.org/release/manualpages/DMSwarm/DMSwarmGetCellSwarm/</a></div>
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Best,</div>
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Joe</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> MIGUEL MOLINOS PEREZ <mmolinos@us.es><br>
<b>Sent:</b> Thursday, May 8, 2025 10:22 AM<br>
<b>To:</b> Matthew Knepley <knepley@gmail.com><br>
<b>Cc:</b> petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov>; Joseph Pusztay <josephpu@buffalo.edu><br>
<b>Subject:</b> Re: [petsc-users] Problems with the null-space removal</font>
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<div>This function “ DMSwarmCreatreSubswarm” is published somewhere? I can’t find it in the main branch of PETSc.
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<div>Thanks,</div>
<div>Miguel<br>
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<div>On May 6, 2025, at 9:03 AM, MIGUEL MOLINOS PEREZ <mmolinos@us.es> wrote:</div>
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<div class="x_gmail_quote x_gmail_quote_container">Oh, so you want to turn off some Swarm nodes? Joe has a DMSwarmCreatreSubswarm() function somewhere. This might work.</div>
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<div class="x_gmail_quote x_gmail_quote_container">This would be awesome! </div>
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<div class="x_gmail_quote x_gmail_quote_container">Thanks,</div>
<div class="x_gmail_quote x_gmail_quote_container">Miguel</div>
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<div>On 5 May 2025, at 21:43, Matthew Knepley <knepley@gmail.com> wrote:</div>
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<div dir="ltr">On Mon, May 5, 2025 at 2:08 PM MIGUEL MOLINOS PEREZ <<a href="mailto:mmolinos@us.es">mmolinos@us.es</a>> wrote:</div>
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<div>Hi Matt, thank you for your response!<br id="x_m_-1640743572746169310lineBreakAtBeginningOfMessage">
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<div>The most likely thing is that the nullspace is slightly wrong, or the convergence test is not accounting for the nullspace somehow.</div>
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<div>However, since so many equations are inactive, I would consider projecting the problem. I might either</div>
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<div>1) Select a subset of the mesh to phrase the problem on. In you use DMPlex, you could use DMPlexFilter().</div>
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<div>I’am using a DMSwarm mesh so I can’t use this function.</div>
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<div>Oh, so you want to turn off some Swarm nodes? Joe has a DMSwarmCreatreSubswarm() function somewhere. This might work.</div>
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<div>2) Use a constraint to get a subsystem for Newton using SNESVI. The SNESVIRS will project the linear system onto a subspace without the constraints.</div>
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<div>I assume you meant <span style="color:rgb(44,54,63); background-color:rgb(255,255,255)"><b>SNESVINEWTONRSLS (former SNESVI)</b></span>.</div>
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<div>This is a subtype of SNESVI as it is a particular implementation.</div>
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<div>I’ve been digging on this approach. However,I don’t think this fits my problem since I can not define the list of active nodes using upper and lower limits like in:</div>
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<div>The way I am thinking, you must have some test to determine what nodes are active. I was supposing that test depending on the solution at those nodes. If that is true, you can use that test as the constraint.</div>
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<div> Thanks,</div>
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<div>Thanks,</div>
<div>Miguel</div>
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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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