CPXMIP_OPTIMAL_TOL

An optimal solution within the tolerance defined by the relative or absolute MIP gap has been found.

CPLEX returns CPXMIP_OPTIMAL_TOL when the current solution has not been proven optimal but appears optimal within the tolerances of the relative or absolute MIP gap, as set by the parameters relative MIP gap tolerance or absolute MIP gap tolerance. CPLEX can return CPXMIP_OPTIMAL instead even when the MIP gap tolerances are strictly greater than 0 (zero). Examples where CPLEX can prove optimality of a solution include finding a solution of a feasibility problem where no objective function is defined, or finding a solution that has a value equal to the current dual bound. (In that case, the gap is exactly 0 (zero).)