Mapping methods between XPRBctr and new class Inequality

Sorry, for the late reply. It is probably best to look at the examples that ship in the examples/solver/optimizer/cxx/objects directory and at the introduction here.

The way to build a linear constraint in the C++ API involves these steps:

1. Create expressions for the left-hand side and right-hand side.
2. Use relational operators to turn this into an inequality definition.
3. Use XpressProblem::addConstraint() to add this as a constraint. This function returns a handle to the newly added constraint, an instance of xpress::objects::Inequality.
4. You can then later change coefficients in this constraint (directly in the matrix) use the chgCoef(), chgCoefs() and setRhs() functions of class Inequality.

Here is a short example:

#include <xpress.hpp>
#include <xpress_objects.hpp>
 
using namespace xpress::objects;
 
int
main(void)
{
  XpressProblem prob;
  auto x = prob.addVariables(3).toArray();
  Expression lhs = x[0] + 2*x[1];         // Create expression for left-hand side.
  Expression rhs = x[2] + 4;              // Create expression for right-hand side.
  auto def = lhs <= rhs;                  // Create constraint _definition_.
  Inequality i = prob.addConstraint(def); // Create an actual constraint from the definition.
  prob.writeProb("p1.lp"); // LP file has: R1: C1 + 2 C2 - C3 <= 4
  i.chgCoef(x[1], 3);                     // Modify the constraint.
  prob.writeProb("p2.lp"); // LP file has: R1: C1 + 3 C2 - C3 <= 4 
  return 0;
}