On to., 2008-09-25 at 10:20 +0200, Jed Brown wrote: > On Wed 2008-09-24 19:36, Nuno David Lopes wrote: > > Also another doubt, (i'm guessing that is my math ignorance only) > > is it usual that PETSc::gmres with hypre::amg preconditioner doesn't work. > > (After reading that it is so powerfull...) > > In a Stokes 566000^2 subsystem it simply blows up with all of the RAM > > memory > > (16Gb). > > (I tried it with simpler problems but with bigger systems and it worked > > perfectly, converging in <10 iterations.) > > The Stokes problem is indefinite, hence normal preconditioners are not > expected to work. Reordering unknowns and diagonal shifts can help, but > you really want a Schur complement preconditioner or Vanka smoothers for > multigrid (not conveniently available). The easiest thing is to > assemble the matrix > > P1 = (A B') or P2 = (A 0) > (0 M ) (0 M) > > (where M is the mass matrix) to precondition the Stokes system > > (A B') (u) = (f) > (B 0 ) (p) (0) > > Unfortunately, Dolfin does not have the plumbing in place for separate > preconditioning matrices so you will need to work with the KSP directly. > > Jed
You can do it from Python toghether with PyTrilinos though. The code is under the sandbox /dolfin/sandbox/la/trilinos/demo5.py Kent _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
