[petsc-users] malconfigured gamg

[Arne Morten Kvarving]

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))

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