[petsc-users] DIVERGED_INDEFINITE_PC in algebraic multigrid

[Michele Rosso]

Mark,

thank you for your input and sorry my late reply: I saw your email only now.
By setting up the solver each time step you mean re-defining the KSP 
context every time? Why should this help?
I will definitely try that as well as the hypre solution and report back.
Again, thank you.

Michele

On 05/22/2014 09:34 AM, Mark Adams wrote:
> If the solver is degrading as the coefficients change, and I would 
> assume get more nasty, you can try deleting the solver at each time 
> step.  This will be about 2x more expensive, because it does the setup 
> each solve, but it might fix your problem.
>
> You also might try:
>
> -pc_type hypre
> -pc_hypre_type boomeramg
>
>
>
>
> On Mon, May 19, 2014 at 6:49 PM, Jed Brown <jed at jedbrown.org 
> <mailto:jed at jedbrown.org>> wrote:
>
>     Michele Rosso <mrosso at uci.edu <mailto: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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