[petsc-users] on SNESSetJacobian semantics

[Matthew Knepley]

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.

  Matt


> Why then are there not two monomorphic "SetJacobian" functions, one for
> linear maps that wouldn't require recomputation and one for every other
> case ?
>
> Coming from a functional background, I find reasoning with "NULL" to be
> very error-prone.
>
> Thank you,
> Marco
>



-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20151022/c493a3ee/attachment.html>