[petsc-users] Context behind SNESComputeFunction call

[Kong, Fande]

On Mon, Jan 8, 2018 at 2:15 PM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>
> > On Jan 8, 2018, at 2:59 PM, Alexander Lindsay <alexlindsay239 at gmail.com>
> wrote:
> >
> > Is there any elegant way to tell whether SNESComputeFunction is being
> called under different conceptual contexts?
> >
> > E.g. non-linear residual evaluation vs. Jacobian formation from finite
> differencing vs. Jacobian-vector products from finite differencing?
>
>   Under normal usage with the options database no.
>

Hi Barry,

How difficult to provide an API? Is it possible?



>
>   If you have some reason to know you could write three functions and
> provide them to SNESSetFunction(), MatMFFDSetFunction(), and
> MatFDColoringSetFunction(). Note that these functions have slightly
> different calling sequences but you can have all of them call the same
> underlying common function if you are only interested in, for example, how
> many times the function is used for each purpose.
>

If we use this way for the Jacobian-free Newton, the function evaluation
will be called twice at the first linear iteration because the computed
residual vector at the nonlinear step  is not reused. Any way to reuse the
function residual of the Newton step instead of recomputing a new residual
at the first linear iteration?

Fande,



>
>    Barry
>
>
>
> >
> > Alex
>
>
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