On Tue, Dec 16, 2025 at 12:39 PM MIGUEL MOLINOS PEREZ <[email protected]>
wrote:
>
> Dear all,
>
> 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).
>
>
> For those DOF 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).
>
> 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.
>
>
> 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 q_(i,n)
> is the position of the particle at the previous configuration.
>
This puts a 1 on the diagonal, which is usually what you want (esp for
particle problems).
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.
Thanks,
Matt
> Best regards,
>
> Miguel
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!a9ge_7Blw6FP4XR8osFatvOvy7Q2pdIyLX8lVZs3eFcKKQhLJ0TRkrPMAXOBllnlR6EP1Oa_qkH_pcJzgpX-$
<https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!a9ge_7Blw6FP4XR8osFatvOvy7Q2pdIyLX8lVZs3eFcKKQhLJ0TRkrPMAXOBllnlR6EP1Oa_qkH_pf-AU3HW$
>
