[petsc-users] example on manually setup matrix coloring for finite difference Jacobian?

[Zou (Non-US), Ling]

(meant to send to the list)

Thanks Matt for you reply.

In my case, 2-d problem with unstructured mesh, what would be a
practical way to move forward?
1, using fully analytical Jacobian, it however will be very difficult
to make everything right eventually
2, using finite differencing Jacobian, but use keyword
SNESDefaultComputeJacobian, which is very slow
3, using matrix free operation to avoid the Jacobian calculation
Any suggestion?

On Wed, Jul 17, 2013 at 5:06 PM, Matthew Knepley <knepley at gmail.com> wrote:
> On Wed, Jul 17, 2013 at 6:02 PM, Zou (Non-US), Ling <ling.zou at inl.gov>
> wrote:
>>
>> Hi All,
>>
>> If I have a 2-d problem with unstructured triangle mesh, I suppose I
>> need handle the coloring manually in case I need the finite
>> differencing Jacobian. Also I guess it is doable as I know the mesh
>> connectivity. I noticed there are several examples handling structured
>> mesh case. Is there any example to setup the matrix coloring for this
>> kind of case?
>
>
> We have no examples of this, and have not pushed it in our development. I
> would also consider forming a simplified operator for preconditioning while
> using the finite difference approximation for the action.
>
>    Matt
>
>>
>> Best,
>>
>> Ling
>
>
>
>
> --
> 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