[petsc-users] DIVERGED_INDEFINITE_PC in algebraic multigrid

[Jed Brown]

Michele Rosso <mrosso at uci.edu> writes:

> Jed,
>
> thank you very much!
> I will try with ///-mg_levels_ksp_type chebyshev -mg_levels_pc_type 
> sor/   and report back.
> Yes, I removed the nullspace from both the system matrix and the rhs.
> Is there a way to have something similar to Dendy's multigrid or the 
> deflated conjugate gradient method with PETSc?

Dendy's MG needs geometry.  The algorithm to produce the interpolation
operators is not terribly complicated so it could be done, though DMDA
support for cell-centered is a somewhat awkward.  "Deflated CG" can mean
lots of things so you'll have to be more precise.  (Most everything in
the "deflation" world has a clear analogue in the MG world, but the
deflation community doesn't have a precise language to talk about their
methods so you always have to read the paper carefully to find out if
it's completely standard or if there is something new.)
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