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

On Thu, 21 Jul 2005, Mario Mendez wrote:

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.

I am not completely clear. If you mean that you want to insert two dimensions between the "B" and "C" dimensions, and rename the "E" dimension as "G", then here is a snippet of Prolog that does this.

T = c, ppl_new_Polyhedron_from_space_dimension(T, 5, universe, P), ppl_Polyhedron_add_constraints(P, [B = 2, E = 8]), ppl_Polyhedron_add_space_dimensions_and_embed(P, 2), ppl_Polyhedron_map_space_dimensions(P, [A-A, B-B, C-E, D-F, E-G, F-C, G-D]), ppl_new_Polyhedron_from_space_dimension(T, 7, universe, Q), ppl_Polyhedron_add_constraints(Q, [B = 2, G = 8]), ppl_Polyhedron_equals_Polyhedron(P, Q).

Basically, I have added the 2 new dimensions to the end and then use the "map_space_dimensions" predicate to rearrange the order of the dimensions.

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

Best wishes, Pat

Mario Mendez wrote:

Thanks! It's true that you already answered the question but I was looking for an example....

Dear Mario,

the file interfaces/Prolog/tests/pl_check.pl contains examples of usage for all the Prolog interface predicates. Is this the kind of example you are looking for? All the best,

Roberto