[petsc-users] Help with ML/BoomerAMG

[Gaetan Kenway]

For the forward solve I use ASM+ILU in the same manner as for the adjoint
problem.
The  ASM not a bottleneck  per se. Typically we see the  adjoint problem
taking the same amount of time as the non-linear problem for well-behaved
flows, and the adjoint is shorter for  less well-behaved flows.

The real problem I am having is for certain RANS cases, the
frozen turbulence adjoint is extremely difficult to solve --- requiring
 GMRES subspace sizes on the order of 400-500 to converge.  That's why I
was investigating alternative preconditioning methods that could
help  solve these problems more efficiently.

Gaetan

On Mon, Apr 29, 2013 at 10:16 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Gaetan Kenway <gaetank at gmail.com> writes:
>
> > The problems I am looking at are steady state or quasi-steady state (time
> > spectral approach). The example I sent before was steady state.  The
> > nonlinear solver uses FAS multigrid (only used for full multigrid and
> > start-up on the fine grid) followed by an inexact Newton-Krylov method.
>
> Is NK preconditioned by linear MG?
>
> Is the ASM preconditioner for the adjoint problem a bottleneck compared
> to the forward solve?
>
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