Dear Barry, dear Dave, THANK YOU! You two pointed out the right problem.By using the options you provided (-fieldsplit_0_ksp_type gmres -fieldsplit_0_ksp_pc_side right -fieldsplit_1_ksp_type gmres -fieldsplit_1_ksp_pc_side right), the solver converges in 3 iterations whatever the size of the communicator. All the trick is in the precise resolution of the Schur complement, by using a Krylov method (and not only preonly) *and* applying the preconditioner on the right (so evaluating the convergence on the unpreconditioned residual).
@Barry : the difference you see on the nonzero allocations for the different runs is just an artefact : when using more than one proc, we slighly over-estimate the number of non-zero terms. If I run the same problem with the -info option, I get extra information : [2] MatAssemblyEnd_SeqAIJ(): Matrix size: 110 X 110; storage space: 0 unneeded,5048 used [1] MatAssemblyEnd_SeqAIJ(): Matrix size: 271 X 271; storage space: 4249 unneeded,26167 used [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 307 X 307; storage space: 7988 unneeded,31093 used [2] MatAssemblyEnd_SeqAIJ(): Matrix size: 110 X 244; storage space: 0 unneeded,6194 used [1] MatAssemblyEnd_SeqAIJ(): Matrix size: 271 X 233; storage space: 823 unneeded,9975 used [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 307 X 197; storage space: 823 unneeded,8263 used And 5048+26167+31093+6194+9975+8263=86740 which is the number of exactly estimated nonzero terms for 1 proc. Thank you again! Best regards, Nicolas 2017-01-05 1:36 GMT+01:00 Barry Smith <[email protected]>: > > There is something wrong with your set up. > > 1 process > > total: nonzeros=140616, allocated nonzeros=140616 > total: nonzeros=68940, allocated nonzeros=68940 > total: nonzeros=3584, allocated nonzeros=3584 > total: nonzeros=1000, allocated nonzeros=1000 > total: nonzeros=8400, allocated nonzeros=8400 > > 2 processes > total: nonzeros=146498, allocated nonzeros=146498 > total: nonzeros=73470, allocated nonzeros=73470 > total: nonzeros=3038, allocated nonzeros=3038 > total: nonzeros=1110, allocated nonzeros=1110 > total: nonzeros=6080, allocated nonzeros=6080 > total: nonzeros=146498, allocated nonzeros=146498 > total: nonzeros=73470, allocated nonzeros=73470 > total: nonzeros=6080, allocated nonzeros=6080 > total: nonzeros=2846, allocated nonzeros=2846 > total: nonzeros=86740, allocated nonzeros=94187 > > It looks like you are setting up the problem differently in parallel and > seq. If it is suppose to be an identical problem then the number nonzeros > should be the same in at least the first two matrices. > > > > > On Jan 4, 2017, at 3:39 PM, Karin&NiKo <[email protected]> wrote: > > > > Dear Petsc team, > > > > I am (still) trying to solve Biot's poroelasticity problem : > > <image.png> > > > > I am using a mixed P2-P1 finite element discretization. The matrix of > the discretized system in binary format is attached to this email. > > > > I am using the fieldsplit framework to solve the linear system. Since I > am facing some troubles, I have decided to go back to simple things. Here > are the options I am using : > > > > -ksp_rtol 1.0e-5 > > -ksp_type fgmres > > -pc_type fieldsplit > > -pc_fieldsplit_schur_factorization_type full > > -pc_fieldsplit_type schur > > -pc_fieldsplit_schur_precondition selfp > > -fieldsplit_0_pc_type lu > > -fieldsplit_0_pc_factor_mat_solver_package mumps > > -fieldsplit_0_ksp_type preonly > > -fieldsplit_0_ksp_converged_reason > > -fieldsplit_1_pc_type lu > > -fieldsplit_1_pc_factor_mat_solver_package mumps > > -fieldsplit_1_ksp_type preonly > > -fieldsplit_1_ksp_converged_reason > > > > On a single proc, everything runs fine : the solver converges in 3 > iterations, according to the theory (see Run-1-proc.txt [contains > -log_view]). > > > > On 2 procs, the solver converges in 28 iterations (see Run-2-proc.txt). > > > > On 3 procs, the solver converges in 91 iterations (see Run-3-proc.txt). > > > > I do not understand this behavior : since MUMPS is a parallel direct > solver, shouldn't the solver converge in max 3 iterations whatever the > number of procs? > > > > > > Thanks for your precious help, > > Nicolas > > > > <Run-1-proc.txt><Run-2-proc.txt><Run-3-proc.txt><1_Warning.txt> > >
