On Wed, Jun 29, 2011 at 2:48 PM, tuane <tuane at lncc.br> wrote: > Thank you for your help. > Well, but if the redundant preconditioner uses a direct solve what means: > 1. number of iterations diversify with tolerance
2. reductions iterations with the use the KSPSetInitialGuessNonzero. > When I use the jacobi preconditioner, the number of iterations remains > high. > Redundant runs SOME preconditioner redundantly. If you specify nothing, it runs the default which is GMRES/ILU(0). You can always use -ksp_view to see what you used. Matt > What about tolerance? when I use jacobi preconditioner I need of a > tolerance =1.0e-14 for to obtain the same result when I use the redundant > preconditioner with tolerance=1.0e-10. I think that the tolerance is too > small for jacobi preconditioner. What do you think? > > Thanks again. > Tuane > > > > On Tue, 28 Jun 2011 14:00:06 -0500, Jed Brown wrote: > >> On Tue, Jun 28, 2011 at 11:55, tuane 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 a >> >> . 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 gri >>> >> ould 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. >> >> Links: >> ------ >> [1] mailto:tuane at lncc.br >> > > -- 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/20110629/d96671d9/attachment.html>
