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
pgpU2Z8fXuUVu.pgp
Description: PGP signature
_______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
