How it works¶

When testing a solution for an optimization model, there are several possible cases:

The solution is feasible but possibly suboptimal
The solution is infeasible and:
   a. You want an explanation why it's infeasible
   b. You want to repair the solution
   c. You want to repair the model

This tool can diagnose all of these cases. Note that the difference between cases 2b and 2c is a policy decision: in case of infeasibility, you need to determine whether you want to repair the solution or the model.

Case 1: The solution is feasible but possibly suboptimal¶

First, the solution checker verifies that the given solution satisfies the constraints. If so, it will also compute an optimal solution, to show how far the given solution is from optimal. If you write a .sol solution file, you can see the difference from the given solution and an optimal solution.

Case 2a: The solution is infeasible and you want an explanation¶

If the solution checker verifies that the given solution does not satisfy the model constraints, you can use it to find a set of constraints that conflicts with the given solution. This is done by setting infmethod to I, which calls IIS to find a set of constraints that conflicts with the given solution. Note that if there are multiple independent sets of constraints that conflict, this will only find one set of conflicts; to check for others, remove the infeasible constraints from the model and try again.

Case 2b: The solution is infeasible and you want to repair the solution¶

If the solution checker verifies that the given solution does not satisfy the model constraints, you can use it to modify the solution to make it feasible. This is done by setting infmethod to V, which calls feasRelax to find the smallest changes to the solution values that make the constraints feasible.

Case 2c: The solution is infeasible and you want to repair the model¶

If the solution checker verifies that the given solution does not satisfy the model constraints, you can use it to modify the solution to make it feasible. This is done by setting infmethod to C, which calls feasRelax to find the smallest changes to the constraints that make the solution feasible.