[petsc-dev] controlling vector values while doing matrix free operations

[Dmitry Karpeev]

On Wed, Dec 14, 2011 at 9:45 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Wed, Dec 14, 2011 at 19:40, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>
>> The trouble is that the constraints can get "eliminated" only when they
>> become active.
>
>
> That's not what I meant. I meant to transform the algebraic system so that
> those extra variables were eliminated. The point is that we tend to put a
> lot of effort into designing effective preconditioners for a standard
> formulation (e.g. conservative variables), and that is partly lost of we
> have this other system in which the evaluations of constitutive relations
> are added explicitly.
>
I guess I'm missing something: why would you add pressure to the set of
conservative variables?  It's redundant, as it can be obtained at any time
via the equation of state. The only reason to add it is to impose a bound
constraint on it and use it to monitor for departures from the feasible
set.  If you want to eliminate it, you are better off not adding it in the
first place, it seems to me.

Dmitry.
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