[petsc-users] Finite difference approximation of Jacobian

[Matthew Knepley]

On Mon, Dec 13, 2021 at 1:16 PM Dave May <dave.mayhem23 at gmail.com> wrote:

>
>
> 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.
>

Ah, thanks Dave.

Okay, we should fix that.It is perfectly possible to compute the nonzero
pattern from the DMStag information.

Paging Patrick :)

  Thanks,

    Matt


> 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/>
>>
>

-- 
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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