[petsc-users] confused by the converged reason output

[Matthew Knepley]

On Fri, Jul 19, 2019 at 11:14 AM Michael Wick via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> 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.
>

Can you run with -ksp_converged_reason?

  Thanks,

     Matt


> 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
>
>
>

-- 
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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