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? > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130429/4ad57bf6/attachment.html>
