[petsc-users] PETSc interface to MueLu

[Jed Brown]

victor.magri at dicea.unipd.it writes:

> I suppose that MueLu would give a cleaner implementation of ML's
> features and possibly give a faster code. 

Last I heard, the MueLu implementation was slower.  I don't know if that
has been fixed more recently, but we would be more motivated to write
the interface _after_ they demonstrate some clear benefit in a direct
comparison.

> Also, as it supports the Kokkos library, we would have the possibility
> to run on MPI+threads or MPI+GPU. However, I think that implementing
> an interface for this could be a problem since PETSc works better with
> pure MPI, please correct me if I am wrong about this.

There's a fair chance their code also works better with pure MPI.
(There's no fundamental reason why MPI+threads should be faster than
MPI-only, and some reasons why it could be slower.)  That said, you can
see lots of implementation artifacts on particular machines or for
particular implementations.  Anyway, there is nothing preventing an
interface except the opportunity cost of working on something with such
dubious expected value and zero research value, versus things with
immediate, direct impact.

> Anyway, if it were possible, I just would like to try both multigrid
> implementations through PETSc and see how they behave. 

Patches welcome. (In the short term, and in lieu of some convincing
demonstration.)
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