KSPPREONLY

[Ryan Yan]

Thanks a lot,
Yan

On Mon, Dec 14, 2009 at 11:23 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

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