Stefano Zampini <[email protected]> writes: > In case of BDDC coarse problem, I will not expect strongly unymmetricity. > The coarse problem is also structurally symmetric.
Okay, Chebyshev should just work. I recommend not turning on the "hybrid" stuff because that makes the operator nonlinear and doesn't help much in my experience, particularly as a coarse solver. > Sorry, my fault. I didn't explain completely my point. My intent is not of > changing the default of the coarse solver (which is > ksppreonly+pcredundant), but to find a good ksp in case the user requests a > multilevel bddc, i.e. to solve the coarse problem with another level of > BDDC. In that case, I would choose very few iterations of a cheap ksp (like > richardson or cheby). Okay. > It seems to me that the rational can be: use cheby if the problem is > positive (semi-) definite, and gmres if not. Suggestions? Sure, but note that GMRES is a nonlinear operator unless you converge it to high accuracy. Better is to recursively restrict the coarse space to smaller process sets (like we do in PCGAMG).
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