ksp_monitor and hypre/boomeramg

[Shao-Ching Huang]

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?

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

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$ uname -a
Linux n125 2.6.18-92.1.6.el5 #1 SMP Wed Jun 25 13:45:47 EDT 2008
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