KSPPREONLY

[Ryan Yan]

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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