[petsc-users] Preconditioner question ASM vs SOR

[Erik Andreassen]

I have played a bit with preconditioners for the different levels in PCMG, and among others I have tried additive Schwartz (ASM), which does not seem to work very well - especially with no overlap. I'm curious to hear if anyone can explain why ASM with no overlap performs so much worse than SOR?

Thanks,
Erik

PS: I had a previous question about setting levels in GAMG, and my first impression is (in line with what Mark Adams wrote) that it is better to leave it to figure it out automatically. Also when using it as the coarse level preconditioner in a PCMG.
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