[petsc-users] projection methods in TS

[Matthew Knepley]

On Sat, Feb 4, 2017 at 7:44 PM, Jed Brown <jed at jedbrown.org> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
>
> > On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <hongzhang at anl.gov> wrote:
> >
> >> Can you elaborate a bit more on your problem?
> >>
> >> If your problem is an index-1 DAE, there is no need to use a projection
> >> method, and it is perfectly fine to set it up as a DAE in PETSc. For
> >> high-index DAEs, you may have to use TSSetPostStep() to implement your
> own
> >> projection algorithm.
> >>
> >
> > Please define index.
>
> Think of it as a measure of singularity of the "mass matrix".  Higher
> index DAE have more complicated constraints on compatibility of initial
> conditions.  It's covered in any book or paper on DAEs.
>

Both your explanation and Hong's use of the term do not help Gideon (or me)
know whether he has an index-1 DAE. There has
to be some simple form you can write down so that we can tell.

   Matt

-- 
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
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