[petsc-users] CG with right preconditioning supports NONE norm type only

[Kong, Fande]

Thanks Barry,

We are using "KSPSetPCSide(ksp, pcside)" in the code.  I just tried
"-ksp_pc_side right", and petsc did not error out.

I like to understand why CG does not work with right preconditioning?
Mathematically, the right preconditioning does not make sense?

Fande,

On Wed, Mar 8, 2017 at 9:33 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Please tell us how you got this output.
>
>   PETSc CG doesn't even implement right preconditioning. If you ask for it
> it should error out. CG supports no norm computation with left
> preconditioning.
>
>    Barry
>
> > On Mar 8, 2017, at 10:26 AM, Kong, Fande <fande.kong at inl.gov> wrote:
> >
> > Hi All,
> >
> > The NONE norm type is supported only when CG is used with a right
> preconditioner. Any reason for this?
> >
> >
> >
> > 0 Nonlinear |R| = 1.732051e+00
> >       0 Linear |R| = 0.000000e+00
> >       1 Linear |R| = 0.000000e+00
> >       2 Linear |R| = 0.000000e+00
> >       3 Linear |R| = 0.000000e+00
> >       4 Linear |R| = 0.000000e+00
> >       5 Linear |R| = 0.000000e+00
> >       6 Linear |R| = 0.000000e+00
> >  1 Nonlinear |R| = 1.769225e-08
> >       0 Linear |R| = 0.000000e+00
> >       1 Linear |R| = 0.000000e+00
> >       2 Linear |R| = 0.000000e+00
> >       3 Linear |R| = 0.000000e+00
> >       4 Linear |R| = 0.000000e+00
> >       5 Linear |R| = 0.000000e+00
> >       6 Linear |R| = 0.000000e+00
> >       7 Linear |R| = 0.000000e+00
> >       8 Linear |R| = 0.000000e+00
> >       9 Linear |R| = 0.000000e+00
> >      10 Linear |R| = 0.000000e+00
> >  2 Nonlinear |R| = 0.000000e+00
> > SNES Object: 1 MPI processes
> >   type: newtonls
> >   maximum iterations=50, maximum function evaluations=10000
> >   tolerances: relative=1e-08, absolute=1e-50, solution=1e-50
> >   total number of linear solver iterations=18
> >   total number of function evaluations=23
> >   norm schedule ALWAYS
> >   SNESLineSearch Object:   1 MPI processes
> >     type: bt
> >       interpolation: cubic
> >       alpha=1.000000e-04
> >     maxstep=1.000000e+08, minlambda=1.000000e-12
> >     tolerances: relative=1.000000e-08, absolute=1.000000e-15,
> lambda=1.000000e-08
> >     maximum iterations=40
> >   KSP Object:   1 MPI processes
> >     type: cg
> >     maximum iterations=10000, initial guess is zero
> >     tolerances:  relative=1e-05, absolute=1e-50, divergence=10000.
> >     right preconditioning
> >     using NONE norm type for convergence test
> >   PC Object:   1 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: Not using more complex smoothers.
> >       HYPRE BoomerAMG: Measure type        local
> >       HYPRE BoomerAMG: Coarsen type        Falgout
> >       HYPRE BoomerAMG: Interpolation type  classical
> >     linear system matrix followed by preconditioner matrix:
> >     Mat Object:     1 MPI processes
> >       type: mffd
> >       rows=9, cols=9
> >         Matrix-free approximation:
> >           err=1.49012e-08 (relative error in function evaluation)
> >           Using wp compute h routine
> >               Does not compute normU
> >     Mat Object:    ()     1 MPI processes
> >       type: seqaij
> >       rows=9, cols=9
> >       total: nonzeros=49, allocated nonzeros=49
> >       total number of mallocs used during MatSetValues calls =0
> >         not using I-node routines
> >
> > Fande,
> >
>
>
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