[petsc-users] confused by the converged reason output

[Michael Wick]

Hi PETSc team:

I am a bit confused by the output of converged reason. I set the relative
tolerance to be 10^{-3}. In my run, I get the monitor true residual to be
as follows.
0 KSP preconditioned resid norm 5.402205955230e-11 true resid norm
9.999870838355e-01 ||r(i)||/||b|| 1.000000000000e+00
    1 KSP preconditioned resid norm 2.240069771831e-12 true resid norm
2.329743436488e-01 ||r(i)||/||b|| 2.329773528226e-01
    2 KSP preconditioned resid norm 3.394412665922e-13 true resid norm
7.296473323081e-02 ||r(i)||/||b|| 7.296567566748e-02
    3 KSP preconditioned resid norm 4.936386334724e-14 true resid norm
1.313944571812e-02 ||r(i)||/||b|| 1.313961543155e-02

And the converged reason is solve converged due to CONVERGED_RTOL
iterations 3. The relative error is quite far from the prescribed
tolerance. Is there something I should know about the stopping criteria?

The ks_view output is
Linear m_fieldsplit_0_ solve converged due to CONVERGED_RTOL iterations 3
KSP Object:(m_fieldsplit_0_) 24 MPI processes
  type: gmres
    GMRES: restart=100, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
    GMRES: happy breakdown tolerance 1e-30
  maximum iterations=100, initial guess is zero
  tolerances:  relative=0.001, absolute=1e-50, divergence=10000
  left preconditioning
  using PRECONDITIONED norm type for convergence test
PC Object:(m_fieldsplit_0_) 24 MPI processes
  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        HMIS
    HYPRE BoomerAMG: Interpolation type  ext+i
  linear system matrix = precond matrix:
  Mat Object:  (m_fieldsplit_0_)   24 MPI processes
    type: mpiaij
    rows=115812, cols=115812
    total: nonzeros=1.34986e+06, allocated nonzeros=1.34986e+06
    total number of mallocs used during MatSetValues calls =0
      not using I-node (on process 0) routines


Thanks,

Mike
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