[PPL-devel] PPL and polyhedra comparisons

[Sebastian Pop]

On Fri, Aug 22, 2008 at 11:23 AM, Roberto Bagnara <bagnara at cs.unipr.it> wrote:
>
> This also remained unanswered (I guess that, on the way back from
> holidays, you found zillions of messages pending... I know it is
> not an easy situation).  If you can clarify the semantics of
> the comparison operation you need, we will add it to the library.

Cool, thanks.

>  /* Compares P1 to P2: returns 0 when the polyhedra don't overlap,
>    returns 1 when p1 >= p2, and returns -1 when p1 < p2.  The ">"
>    relation is the "contains" relation.  */
>
> What should be returned if P1 and P2 do overlap and neither is
> contained into the other?
>

In that case,
if p1 has constraints that are larger than p2, then 1, else -1.

i.e.

if p1 \ (p1 inter p2) is bigger than p2, then 1, else -1.

> Concerning the sort function, we are not sure which place it could
> have in the PPL.  The Pointset_Powerset domain is a set, so the
> ordering is an implementation detail that should not concern
> the client application.  Moreover, a reduced Pointset_Powerset
> never contains two polyhedra one of which is contained
> into the other.

Could you return a "ppl_Polyhedron_t *" vector that contains pointers
to the polyhedra in the set in that "topological order"?

Thanks,
Sebastian