[PPL-devel] Equivalent dimensions

[Mario Mendez]

Thank you! Another question then:

How can I insert dimensions in the middle?
E.G: convert
	[B=2,E=8]  Dim= N
in      [B=2,G=8]  Dim = N + 2
after inserting two "universe" dimensions between the original B and E. 
I already know how to add at the beginning/end, but no idea about how to 
use the library for this particular purpose.

Thanks again

PS: I'm working in a abstract domain based on your library for finding 
linear invariants....

P M Hill wrote:
> On Wed, 20 Jul 2005, Mario Mendez wrote:
> 
>> Hi again,
>>
>> I wonder if there is any way (by using the API) to discover which 
>> dimensions are equal. Right now, I inspect the constraint system 
>> looking for 1*X + -1 *Y = 0, but that 'ad-hoc' solution simply does 
>> not look right. Can you help me? Thanks!
> 
> 
> Hi,
> 
> Inspecting the constraints is definitely not the right way to check if 
> X=Y. There is no guarantee as to the exact form of a constraint system 
> for the polyhedron returned to the user. So the constraint X = Y may be 
> implied by the other constraints but not explicitly in the constraint 
> system.
> 
> (Assuming Prolog, but the solution I think would be similar for the C or 
> C++ API)
> 
> To see if the constraint X = Y is satisfied by all the points in a 
> polyhedron, there is the predicate 
> ppl_Polyhedron_relation_with_constraint/3
> 
> If Poly is your polyhedron and X, Y your dimensions, the query
> ppl_Polyhedron_relation_with_constraint(Poly, X = Y, R).
> will unify R with a list of relations one of which will be "included_in"
> if and only if the constraint X = Y is satisfied by all the points in Poly.
> 
> With regards to your stated problem of finding _which_ dimensions are 
> equal, I do not know of any way other than by checking all the pairs of 
> dimensions X and Y and checking if X = Y holds using a method such as 
> that given above.
> 
> Can you say what it is about your application that led to such a query?
> 
> Best wishes,
>   Pat