Describe

IBM ILOG Dispatcher User's Manual > The Basics > Multiple Tours per Vehicle > Describe

Describe

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The problem presented here is similar to a standard VRP, except that each vehicle can make multiple tours.

Step 1 -

Describe the problem

The first step is to write a natural language description of the problem.

The components of the routing model for this problem are the same as for a standard VRP: vehicles, customers, and a depot. In addition, return visits to the depot are modeled.

Some of the constraints in this problem are the same as those in a standard VRP: vehicle capacity and visit quantities. There are no time windows for visits and no opening or closing times at the depot. However, there is a constraint on the total amount of distance each vehicle can travel.

The objective is to minimize the total cost of the solution. The total cost of the routing plan is the total cost for all vehicles added to any costs related to unperformed visits. In this model, vehicle fixed costs and negative penalty costs for return visits are used to encourage multiple tours per vehicle:

In addition to a cost proportional to the distance traveled, each vehicle also has a fixed cost associated with it. Thus, using fewer vehicles will lower the total cost of the solution.
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.

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