Thank you very much for answering me. It was my fault that I was misunderstood. My question is about this paper "The Parma Polyhedra Library: Toward a Complete Set of Numerical Abstractions for the Analysis and Verification" (
http://bugseng.com/products/ppl/documentation/BagnaraHZ08SCP.pdf)which describes a method to find min and max for a linear programming problem. The author used LP_Problem class which I haven't found in the source code of the PPL. He also suggest (page 13) that the LP Solver is only in the CVS repository.