On Thu, Apr 23, 2009 at 11:07 AM, Nguyen, Hung V ERDC-ITL-MS < Hung.V.Nguyen at usace.army.mil> wrote:
> Hello, > > I tried to solver the SPD linear system with using cg/asm preconditioner > and > found that it doesn't scale well, see table below. Note: it does scale well > with cg/jacobi preconditioner. > > Do you know why it doesn't scale? ILU is incredibly unpredictable. You have not provided the Jacobi numbers, but the particular nonzero pattern of the non-overlapping matrix must be much more amenable. Also, this is a really really bad preconditioner for your system. I would put my time into figuring out why my system is so ill-conditioned and try to formulate a good preconditioner, like an approximate system, etc. Matt > > Thanks, > > -hung > > Number Pes Solver Time (secs) #it > 1 31.317345 544 > 2 263.172225 6959 > 4 734.828840 23233 > 8 805.217591 41250 > 16 611.813716 49262 > 32 345.331928 49792 > 64 212.084555 53771 > > > --- > 1 : aprun -n 1 ./test_matrix_read -ksp_type cg -pc_type asm -pc_asm_type > basic -sub_pc_type ilu -sub_ksp_type preonly -ksp_rtol 1.0e-12 > -ksp_max_it > 100000 > Time in PETSc solver: 31.317345 seconds > The number of iteration = 544 > The solution residual error = 1.658653e-08 > 2 norm 7.885361e-07 > infinity norm 6.738382e-09 > 1 norm 2.124207e-04 > > Application 679466 resources: utime 0, stime 0 > ************************ Beginning new run ************************ > > 2 : aprun -n 2 ./test_matrix_read -ksp_type cg -pc_type asm -pc_asm_type > basic -sub_pc_type ilu -sub_ksp_type preonly -ksp_rtol 1.0e-12 > -ksp_max_it > 100000 > Time in PETSc solver: 263.172225 seconds > The number of iteration = 6959 > The solution residual error = 1.794494e-08 > 2 norm 6.579571e-07 > infinity norm 8.745052e-09 > 1 norm 1.907733e-04 > > -- Here is info about matrix A: > > Computed <structure:nrows> as <178353> > Computed <structure:symmetry> as <0> > Computed <structure:nnzeros> as <3578321> > Computed <structure:max-nnzeros-per-row> as <27> > Computed <structure:min-nnzeros-per-row> as <6> > Computed <structure:left-bandwidth> as <76553> > Computed <structure:right-bandwidth> as <76553> > > > > -- 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-users/attachments/20090423/7c8a7193/attachment.htm>
