Jed has given excellent advice. However, your problems sound small. You should try using a direct solver like MUMPS (with --download-mumps during configure, and -ksp_type preonly -pc_type lu -pc_factor_mat_solver_package mumps during the solve).
Matt On Tue, Jun 28, 2011 at 2:00 PM, Jed Brown <jed at 59a2.org> wrote: > On Tue, Jun 28, 2011 at 11:55, tuane <tuane at lncc.br> wrote: > >> cg+redundant-PC give us the best result, similar to out original direct >> solver. we don't be sure what ?redundant? is. >> > > Redundant means that the whole problem is solved redundantly (using a > direct solver by default) on every process. It only makes sense as a coarse > level solver. > > >> Our response are beeing too dependent of these parameters: >> >> 1. iterative solver (CG, GMRES, BCGS) >> 2. preconditioners (jacobi, redundant, ILU) >> 3. tolerance >> 4. number of processors >> > > At this point, you should always run with -ksp_monitor_true_residual to > make sure that it is really converging. > > We also tried to use the Algebraic Multigrid, but without success. An >> error occurs in the program execution. We used the routines: >> call PCSetType (pc, PCMG, ierr) >> > > This is not algebraic multigrid, it is geometric multigrid. If you use DMDA > to manage the grid, then you could use geometric multigrid here. > > But I think you are using a Raviart-Thomas mixed space in which case the > default interpolants from DMDA are not going to work for you. > > The simplest thing you can do is to use PCFieldSplit to eliminate the > fluxes such that the preconditioner can work with the non-mixed > (H^1-conforming) operator defined in the potential/pressure space. > > > The following won't work right now, but it should work soon. I'm describing > it here for the others on petsc-dev. If you call > > PCFieldSplitSetIS(pc,"u",is_fluxes); > PCFieldSplitSetIS(pc,"p",is_potential); > > and > > -pc_type fieldsplit -pc_fieldsplit_type schur > -fieldsplit_u_pc_type jacobi # The (u,u) block is diagonal for lowest order > RT spaces > -fieldsplit_p_pc_type ml # or other multigrid, uses SIMPLE approximation of > the Schur complement which happens to be exact because the (u,u) block is > diagonal. > > > This won't work right now because PCFieldSplit does not actually call > MatGetSchurComplement() is designed. It would simplify fieldsplit.c to use > MatGetSchurComplement(), but then MatGetSubMatrix() would be called twice > for certain blocks in the matrix, once inside the Schur complement and once > directly from fieldsplit.c. This is why I so want to make a mode in which > the parent retains ownership and the caller gets a (intended to be) > read-only reference when MatGetSubMatrix() and MatGetSchurComplement() are > called. > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20110628/f85c4bbf/attachment.html>
