KSPPREONLY

[Barry Smith]

   Yes

On Dec 14, 2009, at 10:19 PM, Ryan Yan wrote:

> Hi, Barry,
> Thanks a lot.
> So this is equivalent to using ksp richardson +pclu with 1 iteration  
> on the coarse grid, right?
>
> Yan
>
> On Mon, Dec 14, 2009 at 11:16 PM, Barry Smith <bsmith at mcs.anl.gov>  
> wrote:
>
>  preonly means apply the preconditioner to the right hand side only,  
> don't do any iterations. Since LU is the preconditioner in this case  
> preonly means it is using LU as a direct solver.
>
>
>
> On Dec 14, 2009, at 10:09 PM, Ryan Yan wrote:
>
> Hi All,
> I have the following output from -snes_view with the default snes  
> setting., but I don't know what the KSPPREONLY does on the coarse  
> grid. Can anyone provide some hints on this?
>
> Assuming:
> A_{coarse} * e_{coarse}  =r _{coarse}
>
>
> Thanks a lot,
>
> Yan
>
>
> ------------------------------------------------------------------------------
> SNES Object:
>  type: ls
>    line search variant: SNESLineSearchCubic
>    alpha=0.0001, maxstep=1e+08
>  maximum iterations=50, maximum function evaluations=10000
>  tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
>  total number of linear solver iterations=32
>  total number of function evaluations=5
>  KSP Object:
>    type: fgmres
>      GMRES: restart=30, using Classical (unmodified) Gram-Schmidt  
> Orthogonalization with no iterative refinement
>      GMRES: happy breakdown tolerance 1e-30
>    maximum iterations=10000, initial guess is zero
>    tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>    right preconditioning
>  PC Object:
>    type: mg
>      MG: type is FULL, levels=2 cycles=v
>    Coarse gride solver -- level 0 presmooths=1 postsmooths=1 -----
>      KSP Object:(mg_coarse_)
>        type: preonly
>        maximum iterations=1, initial guess is zero
>        tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
>        left preconditioning
>      PC Object:(mg_coarse_)
>        type: lu
>          LU: out-of-place factorization
>            matrix ordering: nd
>          LU: tolerance for zero pivot 1e-12
>          LU: factor fill ratio needed 5.02244
>               Factored matrix follows
>              Matrix Object:
>                type=seqaij, rows=4096, cols=4096
>                package used to perform factorization: petsc
>                total: nonzeros=401152, allocated nonzeros=401152
>                  using I-node routines: found 1024 nodes, limit used  
> is 5
>        linear system matrix = precond matrix:
>        Matrix Object:
>          type=seqaij, rows=4096, cols=4096
>          total: nonzeros=79872, allocated nonzeros=79872
>            using I-node routines: found 1024 nodes, limit used is 5
>    Down solver (pre-smoother) ......
>
>
>