KSPPREONLY

[Ryan Yan]

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) ......
>>
>>
>
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