Mark Adams <mfad...@lbl.gov> writes: > I've not looked at it, and it would be hard to because it is not a well > defined problem. But, if the initial guess is low frequency then it will > give a poor estimate for the highest eigen value.
This is true. > It is not clear to me what the relationship is, generally, of an > initial guess and the solution, spectrally. Initial guesses will > change as the problem evolves but we don't update the eigen estimates. > If the user's initial guess happens to be zero then god knows what > happens. The right hand side is used. You have to explicitly ask to use a nonzero initial guess. > (This is actually the case for the XGC1 code!!!) It adds one more > variable in debugging AMG, which is hard enough as it is. I agree that we should be using a random starting vector for spectral estimates. I'm not overly concerned whether it's a hash of the global ID or a deterministic seed, but let's use something that has been studied. Your suggested "hash function" is way hokey. I'm fine with guaranteeing drand48 and a deterministic seed.
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