<div dir="ltr"><div dir="ltr">On Tue, Dec 16, 2025 at 12:39 PM MIGUEL MOLINOS PEREZ <<a href="mailto:mmolinos@us.es">mmolinos@us.es</a>> wrote:</div><div class="gmail_quote gmail_quote_container"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">



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Dear all, </p>
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I am working with a large nonlinear system solved with SNES, where a significant fraction of the unknowns are temporarily inactive due to a physical parameter being zero (e.g. zero occupancy / zero weight).</p>
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<span style="font-kerning:none">For those DOF </span>the corresponding equilibrium equation is physically inactive, but the unknown still appears in the global vector and in couplings of neighboring particles (Im using dmswarm).</p>
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At the moment, these inactive equations contribute with a zero residual (F_i=0), which (I think) leads to poor conditioning and convergence issues for large problems.</p>
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<span style="font-kerning:none">My question is about best numerical practice in this situation. For the position field, should I do something like F_i = q_i - q_(i,n)? Where </span>q_(i,n) is the position of the particle at the previous configuration.</p></div></div></blockquote><div>This puts a 1 on the diagonal, which is usually what you want (esp for particle problems).</div><div><br></div><div>However, there could be convergence problems with Newton, with these directions swamping other descent directions. That is the argument for eliminating these unknowns. It sounds like it would be worth trying to see if this is the case.</div><div><br></div><div>  Thanks,</div><div><br></div><div>     Matt</div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div>
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Best regards,</p>
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Miguel</p>
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</blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><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><div><br></div><div><a href="https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!a9ge_7Blw6FP4XR8osFatvOvy7Q2pdIyLX8lVZs3eFcKKQhLJ0TRkrPMAXOBllnlR6EP1Oa_qkH_pf-AU3HW$" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><br></div></div></div></div></div></div></div></div>