[petsc-dev] The question about the PETSc example

[Lulu Liu]

Run the example /petsc/src/snes/examples/tutorials/ex28.c using the
following options(found in the makefile)

 ./ex28 -da_grid_x 20 -snes_converged_reason -snes_monitor_short
-problem_type 2

It works using default analytic Jacobian to solve coupled system, however,
I comment

 Line 434 : ierr =
SNESSetJacobian(snes,B,B,FormJacobian_All,user);CHKERRQ(ierr);

and run the code again using the same options (i.e., FD Jacobian instead of
analytic Jacobian), we will get the results:

Nonlinear solve did not converge due to DIVERGED_MAX_IT iterations 50

Could you explain why it does not work using FD Jacobian in this example?

Thanks

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