On Mon, Mar 18, 2019 at 3:56 PM Rossi, Simone via petsc-users < petsc-users@mcs.anl.gov> wrote:
> To follow up on that: when would you want to use gmres instead of fgmres > in the outer ksp? > The difference here is just that FGMRES is right-preconditioned by default, so you do not get the extra application. I think if you use the regular monitor, -ksp_monitor, you will not see 2 applications. Matt > Thanks again for the help, > > Simone > ------------------------------ > *From:* Rossi, Simone > *Sent:* Monday, March 18, 2019 3:43:04 PM > *To:* Justin Chang > *Cc:* Smith, Barry F.; petsc-users@mcs.anl.gov > *Subject:* Re: [petsc-users] BJACOBI with FIELDSPLIT > > > Thanks, using fgmres it does work as expected. > > I thought gmres would do the same since I'm solving the subblocks > "exactly". > > > Simone > > > ------------------------------ > *From:* Justin Chang <jychan...@gmail.com> > *Sent:* Monday, March 18, 2019 3:38:34 PM > *To:* Rossi, Simone > *Cc:* Smith, Barry F.; petsc-users@mcs.anl.gov > *Subject:* Re: [petsc-users] BJACOBI with FIELDSPLIT > > Use -ksp_type fgmres if your inner ksp solvers are gmres. Maybe that will > help? > > On Mon, Mar 18, 2019 at 1:33 PM Rossi, Simone via petsc-users < > petsc-users@mcs.anl.gov> wrote: > > Thanks Barry. > > Let me know if you can spot anything out of the ksp_view > > > KSP Object: 1 MPI processes > > type: gmres > > restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > happy breakdown tolerance 1e-30 > > maximum iterations=5000, nonzero initial guess > > tolerances: relative=0.001, absolute=1e-50, divergence=10000. > > left preconditioning > > using PRECONDITIONED norm type for convergence test > > PC Object: 1 MPI processes > > type: fieldsplit > > FieldSplit with MULTIPLICATIVE composition: total splits = 2, > blocksize = 2 > > Solver info for each split is in the following KSP objects: > > Split number 0 Fields 0 > > KSP Object: (fieldsplit_0_) 1 MPI processes > > type: gmres > > restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > happy breakdown tolerance 1e-30 > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-12, absolute=1e-50, divergence=10000. > > left preconditioning > > using PRECONDITIONED norm type for convergence test > > PC Object: (fieldsplit_0_) 1 MPI processes > > type: hypre > > HYPRE BoomerAMG preconditioning > > Cycle type V > > Maximum number of levels 25 > > Maximum number of iterations PER hypre call 1 > > Convergence tolerance PER hypre call 0. > > Threshold for strong coupling 0.25 > > Interpolation truncation factor 0. > > Interpolation: max elements per row 0 > > Number of levels of aggressive coarsening 0 > > Number of paths for aggressive coarsening 1 > > Maximum row sums 0.9 > > Sweeps down 1 > > Sweeps up 1 > > Sweeps on coarse 1 > > Relax down symmetric-SOR/Jacobi > > Relax up symmetric-SOR/Jacobi > > Relax on coarse Gaussian-elimination > > Relax weight (all) 1. > > Outer relax weight (all) 1. > > Using CF-relaxation > > Not using more complex smoothers. > > Measure type local > > Coarsen type Falgout > > Interpolation type classical > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_0_) 1 MPI processes > > type: seqaij > > rows=35937, cols=35937 > > total: nonzeros=912673, allocated nonzeros=912673 > > total number of mallocs used during MatSetValues calls =0 > > not using I-node routines > > Split number 1 Fields 1 > > KSP Object: (fieldsplit_1_) 1 MPI processes > > type: gmres > > restart=30, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > > happy breakdown tolerance 1e-30 > > maximum iterations=10000, initial guess is zero > > tolerances: relative=1e-12, absolute=1e-50, divergence=10000. > > left preconditioning > > using PRECONDITIONED norm type for convergence test > > PC Object: (fieldsplit_1_) 1 MPI processes > > type: hypre > > HYPRE BoomerAMG preconditioning > > Cycle type V > > Maximum number of levels 25 > > Maximum number of iterations PER hypre call 1 > > Convergence tolerance PER hypre call 0. > > Threshold for strong coupling 0.25 > > Interpolation truncation factor 0. > > Interpolation: max elements per row 0 > > Number of levels of aggressive coarsening 0 > > Number of paths for aggressive coarsening 1 > > Maximum row sums 0.9 > > Sweeps down 1 > > Sweeps up 1 > > Sweeps on coarse 1 > > Relax down symmetric-SOR/Jacobi > > Relax up symmetric-SOR/Jacobi > > Relax on coarse Gaussian-elimination > > Relax weight (all) 1. > > Outer relax weight (all) 1. > > Using CF-relaxation > > Not using more complex smoothers. > > Measure type local > > Coarsen type Falgout > > Interpolation type classical > > linear system matrix = precond matrix: > > Mat Object: (fieldsplit_1_) 1 MPI processes > > type: seqaij > > rows=35937, cols=35937 > > total: nonzeros=912673, allocated nonzeros=912673 > > total number of mallocs used during MatSetValues calls =0 > > not using I-node routines > > linear system matrix = precond matrix: > > Mat Object: () 1 MPI processes > > type: seqaij > > rows=71874, cols=71874 > > total: nonzeros=3650692, allocated nonzeros=3650692 > > total number of mallocs used during MatSetValues calls =0 > > using I-node routines: found 35937 nodes, limit used is 5 > > > ------------------------------ > *From:* Smith, Barry F. <bsm...@mcs.anl.gov> > *Sent:* Monday, March 18, 2019 3:27:13 PM > *To:* Rossi, Simone > *Cc:* petsc-users@mcs.anl.gov > *Subject:* Re: [petsc-users] BJACOBI with FIELDSPLIT > > > Simone, > > This is indeed surprising, given the block structure of the matrix and > the exact block solves we'd expect the solver to converge after the > application of the preconditioner. Please send the output of -ksp_view > > Barry > > Also if you are willing to share your test code we can try running it to > determine why it doesn't converge immediately. > > > > On Mar 18, 2019, at 2:14 PM, Rossi, Simone via petsc-users < > petsc-users@mcs.anl.gov> wrote: > > > > Dear all, > > I'm debugging my application in which I'm trying to use the FIELDSPLIT > preconditioner for solving a 2x2 block matrix. > > > > Currently I'm testing the preconditioner on a decoupled system where I > solve two identical and independent Poisson problems. Using the default > fieldsplit type (multiplicative), I'm expecting the method to be equivalent > to a Block Jacobi solver. > > Setting > > -ksp_rtol 1e-6 > > while using gmres/hypre on each subblock with > > -fieldsplit_0_ksp_rtol 1e-12 > > -fieldsplit_1_ksp_rtol 1e-12 > > I'm expecting to converge in 1 iteration with a single solve for each > block. > > > > Asking to output the iteration count for the subblocks with > > -ksp_converged_reason > > -fieldsplit_0_ksp_converged_reason > > -fieldsplit_1_ksp_converged_reason > > revealed that the outer solver converges in 1 iteration, but each block > is solved for 3 times. > > This is the output I get: > > > > Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 > > Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 > > 0 KSP preconditioned resid norm 9.334948012657e+01 true resid norm > 1.280164130222e+02 ||r(i)||/||b|| 1.000000000000e+00 > > > > Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 > > Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 > > Linear fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 7 > > Linear fieldsplit_1_ solve converged due to CONVERGED_RTOL iterations 7 > > 1 KSP preconditioned resid norm 1.518151977611e-11 true resid norm > 8.123270435936e-12 ||r(i)||/||b|| 6.345491366429e-14 > > > > Linear solve converged due to CONVERGED_RTOL iterations 1 > > > > > > Are the subblocks actually solved for multiple times at every outer > iteration? > > > > Thanks for the help, > > > > Simone > > -- 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 https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
