Returns the slack, or surplus, values for the constraints at the optimal solution. «prog» is a problem specified by DefineOptimization.
As an example, consider the following example constraint:
5 x1 + 3 x2 - x3 <= 14
Suppose the optimal solution is found at (1,2,3). Then the left-hand side of this constraint at the optimum is 8. The slack, therefore, is 14-8 = 6. In other words, the right-hand side coefficient could be decreased by 6 units before the optimal solution would be impacted.
A slack of zero indicates that the constraint is one that is actively constraining the optimal solution.