[petsc-users] on SNESSetJacobian semantics

[Marco Zocca]

Thank you, but this is not really helping;

why are there two slots to supply the Jacobian of the same function, i.e.
Amat and J ?





On 22 October 2015 at 16:30, Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Oct 22, 2015 at 9:20 AM, Marco Zocca <zocca.marco at gmail.com>
> wrote:
>
>> The signature of SNESSetJacobian is
>>
>> PetscErrorCode  SNESSetJacobian(SNES snes,Mat Amat,Mat
>> Pmat,PetscErrorCode (*J)(SNES,Vec,Mat,Mat,void*),void *ctx)
>>
>> however it would seem redundant to supply both a constant matrix and a
>> function to compute the Jacobian.
>> The manual says of J "(if NULL then SNES retains any previously set
>> value": this would only apply to linear functions, is this correct?
>>
>
> It means, if you give NULL, but have previously called SetJacobian() then
> it uses the function pointer previously passed
> rather than setting it to NULL.
>
>
>
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