Barry Smith <[email protected]> writes: >> On Jan 11, 2017, at 3:51 PM, Jed Brown <[email protected]> wrote: >> >> 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). > > Jed, > > Yeah but what about checking that the sum of the number of pre and post > smooths >=1 ?
Usually fine, but what one potential use case is if someone wants to test a more aggressive coarsening strategy. For example, using zero smooths on odd levels would be double-rate coarsening and might be more convenient to implement than the direct operators. (In the strong-scaling limit, it might also be a good communication pattern for reducing the process set.)
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