[petsc-dev] The question about the PETSc example

[Peter Brune]

This is not the full FD Jacobian, but the one constructed by coloring. It's
a hunch, but I'd bet DMComposite doesn't have a proper coloring in place.
This should error out. I'll check out why not.

You don't have to alter the source to do this. You can use
-snes_fd_coloring or -snes_fd.

- Peter

- Peter
On Sep 29, 2013 3:07 PM, "Lulu Liu" <lulu.liu at kaust.edu.sa> wrote:

> 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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