[petsc-users] divergence of quasi-Newton scheme (SNES)

[hg]

Hello

I would expect the setting below would give the same behaviour like
-snes_type newtonls -snes_linesearch_type basic:

-snes_type qn
-snes_qn_type lbfgs
-snes_qn_m 1
-snes_qn_restart_type periodic
-snes_qn_scale_type jacobian
-snes_linesearch_type basic

But it's not, below is the convergence log:
entering BuildRHS
0 SNES Function norm 7.450427214612e+03
entering BuildLHS
entering BuildRHS
  1 SNES Function norm 7.902262148182e+03
entering BuildRHS
  2 SNES Function norm 8.426417730274e+03
    Periodic restart! i_r = 1
entering BuildLHS
entering BuildRHS
  3 SNES Function norm 5.571513092130e+04
entering BuildRHS
  4 SNES Function norm 4.019723509872e+05
    Periodic restart! i_r = 1
entering BuildLHS
entering BuildRHS
  5 SNES Function norm 9.259722791615e+05
entering BuildRHS
  6 SNES Function norm 3.985884724278e+08
Nonlinear solve did not converge due to DIVERGED_DTOL iterations 6

For -snes_type newtonls -snes_linesearch_type basic:

entering BuildRHS
  0 SNES Function norm 7.450427214612e+03
entering BuildLHS
entering BuildRHS
  1 SNES Function norm 1.937109245338e+01
entering BuildLHS
entering BuildRHS
  2 SNES Function norm 8.126736406257e-01
entering BuildLHS
entering BuildRHS
  3 SNES Function norm 1.143237968970e-03
entering BuildLHS
entering BuildRHS
  4 SNES Function norm 2.706184329411e-09
Nonlinear solve converged due to CONVERGED_FNORM_RELATIVE iterations 4

Would it be the parameters not the same? My idea is first starting with a
good configuration of lbfgs then increase the restart (m) to see how the
convergence going (and save time).

Thanks
Giang
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