An improved multiple ant colony system for the collection vehicle routing problems with intermediate facilities

The collection vehicle routing problems with intermediate facilities (CVRP-IF) is actually belong to a well-known generalization of VRP, the Multi-Depot Vehicle Routing Problem with Inter-Depot Routes (MDVRPI), which is a combinatorial optimization problem and holds a central place in reverse logistics management, such as waste collection management. This paper presents an improved multiple ant colony system approach called IMACS algorithm, which possesses a new strategy to construct solutions and update increased pheromone to solve CVRP-IF. As there has not been any algorithm applied for CVRP-IF, so we can only compare our computational results to those produced by stochastic nearest neighbor heuristic algorithm ( denoted by NN ).