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 <[email protected]
<mailto:[email protected]>> wrote:
Michele Rosso <[email protected] <mailto:[email protected]>> 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.)
