[petsc-users] Problems about Line Search

[Yingjie Wu]

Dear Petsc developers:
Hi,
Recently I encounter an error message, but I don't know how to solve it. I
solve a problem of a system of nonlinear equations in which the
coefficients of the system vary with variables. The Args are:
 mpiexec -n 1 ./myprogram -snes_mf_operator -snes_view
-snes_converged_reason -snes_monitor -ksp_converged_reason -ksp_monitor
-ksp_rtol 0.1 -snes_rtol 1e-8 -snes_max_funcs 10000000000 -snes_max_it
10000 -pc_factor_levels 6

The log is :
0 SNES Function norm 2.818062118573e+07
    0 KSP Residual norm 1.967792312615e+05
    1 KSP Residual norm 3.423312208841e+03
  Linear solve converged due to CONVERGED_RTOL iterations 1
  1 SNES Function norm 2.818049788401e+07
    0 KSP Residual norm 1.960830037415e+05
    1 KSP Residual norm 3.458649556419e+03
  Linear solve converged due to CONVERGED_RTOL iterations 1
Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 1
SNES Object: 1 MPI processes
  type: newtonls
  maximum iterations=10000, maximum function evaluations=1410065408
  tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
  total number of linear solver iterations=2
  total number of function evaluations=27
  norm schedule ALWAYS
  SNESLineSearch Object: 1 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: 1 MPI processes
    type: gmres
      restart=30, using Classical (unmodified) Gram-Schmidt
Orthogonalization with no iterative refinement
      happy breakdown tolerance 1e-30
    maximum iterations=10000, initial guess is zero
    tolerances:  relative=0.1, absolute=1e-50, divergence=10000.
    left preconditioning
    using PRECONDITIONED norm type for convergence test
  PC Object: 1 MPI processes
    type: ilu
      out-of-place factorization
      6 levels of fill
      tolerance for zero pivot 2.22045e-14
      matrix ordering: natural
      factor fill ratio given 1., needed 4.29616
        Factored matrix follows:
          Mat Object: 1 MPI processes
            type: seqaij
            rows=11368, cols=11368
            package used to perform factorization: petsc
            total: nonzeros=183764, allocated nonzeros=183764
            total number of mallocs used during MatSetValues calls =0
              not using I-node routines
    linear system matrix followed by preconditioner matrix:
    Mat Object: 1 MPI processes
      type: mffd
      rows=11368, cols=11368
        Matrix-free approximation:
          err=1.49012e-08 (relative error in function evaluation)
          Using wp compute h routine
              Does not compute normU
    Mat Object: 1 MPI processes
      type: seqaij
      rows=11368, cols=11368
      total: nonzeros=42774, allocated nonzeros=56840
      total number of mallocs used during MatSetValues calls =0
        not using I-node routines


I don't know what causes Line_Search to diverge.
The Ksp_rtol setting in the program is very small because I find that
linear-step convergence is not good.

My best wishes for Christmas,
Yingjie
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