[petsc-dev] [petsc-users] Multigrid with defect correction

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>      Do you think this is a reasonable approach or am I missing
>      something fundamental? I am assuming generally for the "higher
>      order" DM the Mat it returns is a MATSHELL or a new matrix class
>      built on "tensor contractions" and that kind of nonsense. I don't
>      want to do all the coding and then have it turn out that it is
>      totally useless for CEED etc.

Well, this is exactly what we do in pTatin.

I would ask, why just two discretizations?  I've always thought a better
interface would be for Mats (and any other operators/functions) to have
optional approximations or supplementary data attached.  We can do this
with PetscObjectCompose, but that's hard to work with in a structured
way.  Anyway, I think I would rather just have the Amat with ability to
attach one or more Pmats.
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