[petsc-dev] sor smoothers

[Jed Brown]

"Mark F. Adams" <mfadams at lbl.gov> writes:
>> PCMGSetResidual (if we continue to support it) should not modify the Mat
>
> I don't see how we can support this if we want to use MatResidual as
> Barry has described.  Certainly without adding a lot more ugly to the
> code.

PCMGResidualDefault would just call MatResidual instead MatMult, then VecAYPX.

I don't have a deep problem with removing it, but I think it's
unnecessary to remove it and is convenient if you aren't in control of
creating the coarse level matrices.  I'm thinking of defect correction
schemes where you want the PCMG to be able to evaluate a high-order
residual.  You could do that by making Amat and Pmat different,
implementing MatResidual on A, and propagating that through the levels,
but I think PCMGSetResidual is more convenient for many.
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