[petsc-users] understanding snes_view output

[Gideon Simpson]

When running something with -snes_monitor and -snes_view, I see two sets of numbers that I'm trying to understand (see below).  

The first is the sequence X SNES Function norm, with X going from 0 to 3.  I had interpreted this as saying that it takes 3 steps of Newton, though perhaps this is not the case.  

The next is "total number of linear solves=4" and "total number of function evaluations=31".  How do these numbers relegate to the SNES Function norm statements?  Also, I was surprised by the number of function evaluations given that I specify a SNESSetJacobian in the problem.

  0 SNES Function norm 7.630295941712e-03 
  1 SNES Function norm 3.340185037212e-06 
  2 SNES Function norm 1.310176068229e-13 
  3 SNES Function norm 1.464821375527e-14 
SNES Object: 4 MPI processes
  type: newtonls
  maximum iterations=50, maximum function evaluations=10000
  tolerances: relative=1e-15, absolute=1e-50, solution=1e-15
  total number of linear solver iterations=4
  total number of function evaluations=31
  norm schedule ALWAYS
  SNESLineSearch Object:   4 MPI processes
    type: bt
      interpolation: cubic
      alpha=1.000000e-04
    maxstep=1.000000e+08, minlambda=1.000000e-12
    tolerances: relative=1.000000e-08, absolute=1.000000e-15, lambda=1.000000e-08
    maximum iterations=40
  KSP Object:   4 MPI processes
    type: gmres
      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
    left preconditioning
    using PRECONDITIONED norm type for convergence test
  PC Object:   4 MPI processes
    type: bjacobi
      block Jacobi: number of blocks = 4
      Local solve is same for all blocks, in the following KSP and PC objects:
    KSP Object:    (sub_)     1 MPI processes
      type: preonly
      maximum iterations=10000, initial guess is zero
      tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
      left preconditioning
      using NONE norm type for convergence test
    PC Object:    (sub_)     1 MPI processes
      type: ilu
        ILU: out-of-place factorization
        0 levels of fill
        tolerance for zero pivot 2.22045e-14
        matrix ordering: natural
        factor fill ratio given 1, needed 1
          Factored matrix follows:
            Mat Object:             1 MPI processes
              type: seqaij
              rows=2, cols=2
              package used to perform factorization: petsc
              total: nonzeros=4, allocated nonzeros=4
              total number of mallocs used during MatSetValues calls =0
                using I-node routines: found 1 nodes, limit used is 5
      linear system matrix = precond matrix:
      Mat Object:       1 MPI processes
        type: seqaij
        rows=2, cols=2
        total: nonzeros=4, allocated nonzeros=10
        total number of mallocs used during MatSetValues calls =0
          using I-node routines: found 1 nodes, limit used is 5
    linear system matrix = precond matrix:
    Mat Object:     4 MPI processes
      type: mpiaij
      rows=2, cols=2
      total: nonzeros=4, allocated nonzeros=20
      total number of mallocs used during MatSetValues calls =0
        using I-node (on process 0) routines: found 1 nodes, limit used is 5

-gideon