[petsc-dev] [petsc-users] Multiple solves with PCMG fail

[Mark Adams]

>
>
>
> My real concern with randomness is that results are not reproducible.
>

My feeling is that this will be small but it will finite in exact
arithmetic, which is not ideal.

If the solve is sensitive to this then I think the you are in trouble
anyway (if a plane craters you don't really care how deep the hole is).

If it did indeed lead to an irreplaceable error then you can look at the
verbose output and see that the failures had lower estimates.  At least it
is debuggable and since it has never actually happened, has it, then I
think we could live with the possibility.



> If convergence is sensitive to the RHS used for the estimate, the last
> thing I want is to be unable to reproduce that failure.  One could
> simply hash the index, but then answers would be different if the
> variables are permuted.
>
> Using the RHS also needs one less vector (not a memory concern for GAMG,
> but the cost is not trivial for HPGMG, for example).
>

You can compute it before you create the RHS, no?  Perhaps we add a
SetVectos(Vec[],numvec) that you call before setup() to if you really care
about memory?
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