[petsc-users] snes + matrix free + coloring

[Zou (Non-US), Ling]

On Fri, Mar 7, 2014 at 4:56 PM, Jed Brown <jed at jedbrown.org> wrote:

> "Zou (Non-US), Ling" <ling.zou at inl.gov> writes:
>
> > Hi Jed,
> >
> > I was searching a topic on preconditioning in the mail list and found
> this
> > email.
> >
> >
> > On Wed, Oct 10, 2012 at 2:55 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> >
> >> Then you aren't using a matrix-free method at all.
> >
> >
> > In case of using SNESDefaultComputeJacobianColor to compute Jacobian
> matrix
> > and mf_operator command, is this exactly what you are describing ('aren't
> > using a matrix-free method at all')?
> >
> > The SNESDefaultComputeJacobianColor I found in lines 149-155 from
> >
> http://www.mcs.anl.gov/petsc/petsc-2.3.3/src/snes/examples/tutorials/ex5.c.html
>
> 1. Please upgrade PETSc.  I don't think we have any links to these
> antique man pages, so I assume you specifically changed the version
> number back rather than landing there accidentally.
>
Hmm... I don't know how come I got this old version document. We are using
version 3.4 I believe. I simply did google
'SNESDefaultComputeJacobianColor' and the first search result linked me
here. I searched 'SNESDefaultComputeJacobianColor' in the petsc 3.4 manual,
and it is not existing.


> 2. It is NOT a matrix-free method because coloring is used to assemble
> the matrix.  It usually doesn't make sense to assemble a matrix using
> coloring, but then not use it to apply the matrix (-snes_mf_operator
> only uses the assembled matrix for preconditioning).
>
I agree...

Ling
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