Arne Morten Kvarving <[email protected]> writes: > hi, > > first, this was an user error and i totally acknowledge this, but i > wonder if this might be an oversight in your error checking: if you > configure gamg with ilu/asm smoothing, and are stupid enough to have set > the number of smoother cycles to 0, your program churns along and > apparently converges just fine (towards garbage, but apparently 'sane' > garbage (not 0, not nan, not inf))
My concern here is that skipping smoothing actually makes sense, e.g., for Kaskade cycles (no pre-smoothing). I would suggest checking the unpreconditioned (or true) residual in order to notice when a singular preconditioner causes stagnation (instead of misdiagnosing it as convergence due to the preconditioned residual dropping). > once i set sor as smoother, i got the error message > > 'PETSC ERROR: Relaxation requires global its 0 positive' which pointed > me to my stupid. > > fixing this made both asm and sor work fine. > > it's all wrapped up in a schur/fieldsplit (it's P2/P1 navier-stokes), > constructed by hand due to "surrounding" reasons. but i don't think > that's relevant as such. i've used 3.6.4 as the oldest and 3.7.4 as the > newest version and behavior was the same. if you want logs et al don't > hesitate to ask for them, but i do not think they would add much. > > cheers > > arnem
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