How are negative penalty costs for return visits used to encourage multiple tours per vehicle?

Suggested Answer

By default, the penalty cost for not performing a visit is IloInfinity, which forces the visit to be performed. In this problem, the return visits to the depot have a small negative penalty cost. If the return visit is performed, there is no additional cost added to the solution. If the return visit is not performed, then there is a small negative penalty cost. This makes not performing the return visit a slightly more favorable decision than performing the return visit, since you are minimizing the total cost. However, the negative penalty is so small that not performing the visit does not greatly affect the overall cost of the solution. This enables Dispatcher to make optimization decisions as to whether additional return visits to the depot are desirable.