[petsc-users] Snes behavior

[Ryan Yan]

Hi All,
I am solving a nonlinear system using snes. The -snes_monitor option has the
following output:

  0 SNES Function norm 2.640163923729e+09
  1 SNES Function norm 1.047643565314e+08
  2 SNES Function norm 1.712732074788e+06
  3 SNES Function norm 1.002169173269e+04
  4 SNES Function norm 1.655878303433e+03
  5 SNES Function norm 3.746498305706e+02
  6 SNES Function norm 8.317435704773e+01
  7 SNES Function norm 1.857639969641e+01
  8 SNES Function norm 4.149691057773e+00
  9 SNES Function norm 9.265604042412e-01
 10 SNES Function norm 2.069527103214e-01
 11 SNES Function norm 4.624186491082e-02
 12 SNES Function norm 1.035558432688e-02
 13 SNES Function norm 2.341362958811e-03
 14 SNES Function norm 5.507445427277e-04
 15 SNES Function norm 1.485123568354e-04
 16 SNES Function norm 5.180043781814e-05
 17 SNES Function norm 2.341966514486e-05
 18 SNES Function norm 1.344936158651e-05
 19 SNES Function norm 1.054812641176e-05
Number of Newton iterations = 19
Converged reason is 4

It looks like the iterate never falls into a quadratic convergence region
before it converges. Is there any hint to understand this behavior?

Thanks a lot,

Yan
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