On 09/19/14 18:56, Aleksandra Jovanovic wrote:
I am interested in starting to use Parma Polyhedra library for my research. I do have a specific problem and I would like to check whether PPL could be used for solving.
I need to compare two linear expression and derive the necessary constraints on the variables such that one of them is minimum/maximum. For example, what should be the relation between x, a and b such that 3x+a+5b is smaller than x+5a+3b (just an example I haven’t paid attention to the actually numbers). Are there functions in PPL that I could use to solve this?
Dear Alexandra,
does the following answer your question?
$ cat p.cc #include <ppl.hh>
using namespace std; using namespace Parma_Polyhedra_Library; using namespace Parma_Polyhedra_Library::IO_Operators;
int main() { NNC_Polyhedron ph(3); Variable A(0); Variable B(1); Variable C(2); ph.add_constraint(3*A + B + 5*C < A + 5*B + 3*C); cout << ph.minimized_constraints() << endl; return 0; } $ g++ -W -Wall p.cc -lppl -lgmpxx -lgmp $ a.out -A + 2*B - C > 0 $
Note that I interpreted "smaller" as "strictly smaller". If strict constraints are not required, using C_Polyhedron instead of NNC_Polyhedron will be more efficient. Please do not hesitate to come back to us (by writing to ppl-devel@cs.unipr.it) if I misinterpreted your question or you need more information. Kind regards,
Roberto