[petsc-users] Finite difference approximation of Jacobian

[Dave May]

On Sat 11. Dec 2021 at 22:28, Matthew Knepley <knepley at gmail.com> wrote:

> On Sat, Dec 11, 2021 at 1:58 PM Tang, Qi <tangqi at msu.edu> wrote:
>
>> Hi,
>> Does anyone have comment on finite difference coloring with DMStag? We
>> are using DMStag and TS to evolve some nonlinear equations implicitly. It
>> would be helpful to have the coloring Jacobian option with that.
>>
>
> Since DMStag produces the Jacobian connectivity,
>

This is incorrect.
The DMCreateMatrix implementation for DMSTAG only sets the number of
nonzeros (very inaccurately). It does not insert any zero values and thus
the nonzero structure is actually not defined.
That is why coloring doesn’t work.

Thanks,
Dave


you can use -snes_fd_color_use_mat. It has many options. Here is an example
> of us using that:
>
>
> https://gitlab.com/petsc/petsc/-/blob/main/src/snes/tutorials/ex19.c#L898
>
>   Thanks,
>
>      Matt
>
>
>> Thanks,
>> Qi
>>
>>
>> On Oct 15, 2021, at 3:07 PM, Jorti, Zakariae via petsc-users <
>> petsc-users at mcs.anl.gov> wrote:
>>
>> Hello,
>>
>> Does the Jacobian approximation using coloring and finite differencing
>> of the function evaluation work in DMStag?
>> Thank you.
>> Best regards,
>>
>> Zakariae
>>
>>
>>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
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