[petsc-users] Convergence Error Debugging with KSP solvers in SNES

[Yang Juntao]

Hello,

I’m working on a nonlinear solver with SNES with handcoded jacobian and function. Each linear solver is solved with KSP solver.
But sometimes I got issues with ksp solver convergence. I tried with finite difference approximated jacobian, but get the same error.

From the iterations, the convergence seems ok at the beginning but suddenly diverged in the last iteration.
Hope anyone with experience on ksp solvers could direct me to a direction I can debug the problem.

iter = 0, SNES Function norm 2.94934e-06
iteration 0 KSP Residual norm 1.094600281831e-06
iteration 1 KSP Residual norm 1.264284474186e-08
iteration 2 KSP Residual norm 6.593269221816e-09
iteration 3 KSP Residual norm 1.689570779457e-09
iteration 4 KSP Residual norm 1.040661505932e-09
iteration 5 KSP Residual norm 5.422761817348e-10
iteration 6 KSP Residual norm 2.492867371369e-10
iteration 7 KSP Residual norm 8.261522376775e-11
iteration 8 KSP Residual norm 4.246401544245e-11
iteration 9 KSP Residual norm 2.514366787388e-11
iteration 10 KSP Residual norm 1.982940267051e-11
iteration 11 KSP Residual norm 1.586470414676e-11
iteration 12 KSP Residual norm 9.866392216207e-12
iteration 13 KSP Residual norm 4.951342176999e-12
iteration 14 KSP Residual norm 2.418292660318e-12
iteration 15 KSP Residual norm 1.747418526086e-12
iteration 16 KSP Residual norm 1.094150535809e-12
iteration 17 KSP Residual norm 4.464287492066e-13
iteration 18 KSP Residual norm 3.530090494462e-13
iteration 19 KSP Residual norm 2.825698091454e-13
iteration 20 KSP Residual norm 1.950568425807e-13
iteration 21 KSP Residual norm 1.227898091813e-13
iteration 22 KSP Residual norm 5.411106347374e-14
iteration 23 KSP Residual norm 4.511115848564e-14
iteration 24 KSP Residual norm 4.063546606691e-14
iteration 25 KSP Residual norm 3.677694771949e-14
iteration 26 KSP Residual norm 3.459244943466e-14
iteration 27 KSP Residual norm 3.263954971093e-14
iteration 28 KSP Residual norm 3.087344619079e-14
iteration 29 KSP Residual norm 2.809426925625e-14
iteration 30 KSP Residual norm 4.366149884754e-01
  Linear solve did not converge due to DIVERGED_DTOL iterations 30


SNES Object: 1 MPI processes
  type: newtonls
  SNES has not been set up so information may be incomplete
  maximum iterations=50, maximum function evaluations=10000
  tolerances: relative=1e-08, absolute=1e-50, solution=1e-08
  total number of linear solver iterations=0
  total number of function evaluations=0
  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=1e-08, absolute=1e-50, divergence=10000.
    left preconditioning
    using DEFAULT norm type for convergence test
  PC Object: 1 MPI processes
    type: fieldsplit
    PC has not been set up so information may be incomplete
      FieldSplit with Schur preconditioner, factorization FULL
      Preconditioner for the Schur complement formed from S itself
      Split info:
      KSP solver for A00 block
          not yet available
      KSP solver for S = A11 - A10 inv(A00) A01
          not yet available
    linear system matrix = precond matrix:
    Mat Object: 1 MPI processes
      type: seqaij
      rows=659, cols=659
      total: nonzeros=659, allocated nonzeros=7908
      total number of mallocs used during MatSetValues calls=0
        not using I-node routines

Regards
Juntao
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20201008/5c9cfcac/attachment-0001.html>