Parma Polyhedra Library: Vertex Enumeration and Floating-Point Arithmetic

Question

I am using the Parma Polyhedra Library (PPL) to do vertex enumeration of a given polyhedron. This has been discussed here. However, i cannot figure out how to use rational numbers instead of integers in the computation.

The code below generates a line segment [0.3,3.7] (convex polyhedron in 1 dimensions), and PPL returns the two integers {0,3}, but i want the rational numbers {0.3,3.7}. How can I advice PPL to use rational numbers (floating point arithmetic)?

    #include <cstddef>
    #include <stdio.h>
    #include "ppl.hh"

    using namespace Parma_Polyhedra_Library;

    int main() {
      Variable x(0);
      C_Polyhedron ph(1);
      ph.refine_with_constraint( x <= 3.7);
      ph.refine_with_constraint( x >= 0.3);

      Generator_System gs = ph.generators();
      for(Generator_System::const_iterator it = gs.begin(); it != gs.end(); it++) {
        const Generator& g = *it;
        std::cout << g.coefficient(x) << std::endl;
      }
      return 0;
    }

Answer 1

ppl expects integers in the definition of its contraints. You will have to scale your inequalities with the common denominator.