[petsc-dev] sor smoothers

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>    How about fixing this? Agreed we should not be requiring people to
>    use MatShell to do this stuff but it sounds you want to work around
>    a current design flaw with PCMG by using PCMGSetResidual. Why not
>    fix the design flaw?

What is the "correct" way to compute coarse operators when the user
wants part Galerkin and part rediscretization?  The user's
(non-Galerkin) matrix assembly function has both Mat slots, and they'll
need to know which one to ignore when PCMG configuration says to make
one or the other Galerkin.

I don't know what is really a good interface for this.  PCMGSetResidual
doesn't seem that inconvenient to me.  (Sure, it's not as nicely
recursive and nestable as you might like in an idealized world, but
matrix-free MG implementations for real problems usually have lots of
constraints anyway.)
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