[PPL-devel] PPL and simplification of polyhedra

[Roberto Bagnara]

Sven Verdoolaege wrote:
> On Mon, Aug 18, 2008 at 05:17:01PM +0200, Roberto Bagnara wrote:
>> Albert Cohen wrote:
>>> The concept is called "gist" in Omega, and simplification under a
>>> context in PolyLib. You'd like to run the simplification with the
>>> assumption that some constraints are already enforced, and only retain
>>> the additional constraints (minimized) to define a given sub-polyhedron.
>> Hi Albert,
>>
>> we need to have a more precise specification of the required operation.
>> In particular, for the simplification of  { A <= 0 } under the context
> 
> I assume you mean { A = 0 } here (as { A <= 0 } is not a subset of {A >= 0}).

I don't follow: why should the first polyhedron (the one to simplify)
be a subset of the second polyhedron (the context)?

>> { A >= 0 }, what do you consider simpler?
>>
>> Possibility 1:  { A <= 0 }
>> Possibility 2:  { A = 0 }.
> 
> I asked the same question on the polylib mailing list many
> years ago but got no answer.

I see.  However, I am interested in understanding the real needs of Cloog
independently from what PolyLib does.
Cheers,

    Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it