ksp_monitor and hypre/boomeramg

[Matthew Knepley]

On Tue, Nov 11, 2008 at 6:16 PM, Shao-Ching Huang <schuang at ats.ucla.edu> wrote:
> Hi,
>
> I am using PETSc-2.3.3p15, compiled with Hypre 2.4.0b, to solve a
> Poisson equation (100x100 mesh) using Hypre's boomeramg. The same
> matrix equation has been solved by PETSc's CG or GMRES successfully.
>
> When I run with "-ksp_monitor" (see below), the iterations show
> convergence and everything seems fine.
>
> When I remove the "ksp_monitor" flag (keeping all other flags the
> same), it takes relatively long time to finish. It appears to me (just
> a guess) that the KSP runs through the default ksp_max_it=10000
> iterations without looking at the residual level (even when
> ksp_rtol=1.e-5).
>
> My question is: why does "-ksp_monitor" change the convergence
> criteria/behavior? Or am I doing something wrong?

Nothing should change. You can try -ksp_converged_reason to see why it
terminates. The best way is to put a breakpoint in KSPDefaultConverged()
and check the convergence test.

  Matt

> Some more details are attached below. Thanks,
>
> Shao-Ching
>
> ---------------------------------
>
> In the following, "solve time" is in seconds.
>
> #### with "-ksp_monitor"
>
> $ mpiexec -np 1 -machinefile mach ./ibm  -ksp_type richardson \
> -pc_type hypre -pc_hypre_type boomeramg -ksp_monitor |grep poisson_solve
>
> [poisson_solve] solve time = 0.043164
>
> The convergence looks like:
>
>  0 KSP Residual norm 1.263975733203e-01
>  1 KSP Residual norm 4.825832685316e-03
>  2 KSP Residual norm 1.980816153418e-04
>  3 KSP Residual norm 9.187303727632e-06
>  4 KSP Residual norm 5.022156966290e-07
>
> #### without "-ksp_monitor"
>
> $ mpiexec -np 1 -machinefile mach ./ibm  -ksp_type richardson \
> -pc_type hypre -pc_hypre_type boomeramg  |grep poisson_solve
>
> [poisson_solve] solve time = 66.463
>
>
> #### without "-ksp_monitor" but set "-ksp_max_it 10"
>
> $ mpiexec -np 1 -machinefile mach ./ibm  -ksp_type richardson \
> -pc_type hypre -pc_hypre_type boomeramg  -ksp_max_it 10 |grep poisson_solve
>
> [poisson_solve] solve time = 0.0682499
>
> --------------------------------------
>
> ksp_view:
>
> KSP Object:
>  type: richardson
>    Richardson: damping factor=1
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:
>  type: hypre
>    HYPRE BoomerAMG preconditioning
>    HYPRE BoomerAMG: Cycle type V
>    HYPRE BoomerAMG: Maximum number of levels 25
>    HYPRE BoomerAMG: Maximum number of iterations PER hypre call 1
>    HYPRE BoomerAMG: Convergence tolerance PER hypre call 0
>    HYPRE BoomerAMG: Threshold for strong coupling 0.25
>    HYPRE BoomerAMG: Interpolation truncation factor 0
>    HYPRE BoomerAMG: Interpolation: max elements per row 0
>    HYPRE BoomerAMG: Number of levels of aggressive coarsening 0
>    HYPRE BoomerAMG: Number of paths for aggressive coarsening 1
>    HYPRE BoomerAMG: Maximum row sums 0.9
>    HYPRE BoomerAMG: Sweeps down         1
>    HYPRE BoomerAMG: Sweeps up           1
>    HYPRE BoomerAMG: Sweeps on coarse    1
>    HYPRE BoomerAMG: Relax down          symmetric-SOR/Jacobi
>    HYPRE BoomerAMG: Relax up            symmetric-SOR/Jacobi
>    HYPRE BoomerAMG: Relax on coarse     Gaussian-elimination
>    HYPRE BoomerAMG: Relax weight  (all)      1
>    HYPRE BoomerAMG: Outer relax weight (all) 1
>    HYPRE BoomerAMG: Using CF-relaxation
>    HYPRE BoomerAMG: Measure type        local
>    HYPRE BoomerAMG: Coarsen type        Falgout
>    HYPRE BoomerAMG: Interpolation type  classical
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=mpiaij, rows=10000, cols=10000
>    total: nonzeros=90000, allocated nonzeros=90000
>      not using I-node (on process 0) routines
>
> --------------------------------------
>
> $ uname -a
> Linux n125 2.6.18-92.1.6.el5 #1 SMP Wed Jun 25 13:45:47 EDT 2008
> x86_64 x86_64 x86_64 GNU/Linux
>
>
>
>
>
>



-- 
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