[petsc-users] BJACOBI with FIELDSPLIT
Matthew Knepley
knepley at gmail.com
Mon Mar 18 14:58:39 CDT 2019
On Mon, Mar 18, 2019 at 3:56 PM Rossi, Simone via petsc-users <
petsc-users at 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 at 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 <jychang48 at gmail.com>
> *Sent:* Monday, March 18, 2019 3:38:34 PM
> *To:* Rossi, Simone
> *Cc:* Smith, Barry F.; petsc-users at 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 at 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. <bsmith at mcs.anl.gov>
> *Sent:* Monday, March 18, 2019 3:27:13 PM
> *To:* Rossi, Simone
> *Cc:* petsc-users at 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 at 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/>
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