KSPPREONLY

[Barry Smith]

   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) ......
>