The Vehicle Routing Problem with Backhauls (VRPB) is an extension of the VRP that deals with two types of customers: the consumers (linehaul) that request goods from the depot and the suppliers (backhaul) that send goods to the depot. In this paper, we propose a simple yet effective iterated local search algorithm for the VRPB. Its main component is an oscillating local search heuristic that has two main features. First, it explores a wide neighborhood structure at each iteration. This is efficiently done using an additional data structure that stores information about the set of neighboring solutions. Second, the heuristic performs constant transitions between feasible and infeasible regions of the solution space. These transitions are regulated by a dynamic adjustment of the penalty applied to infeasible solutions. An extensive statistical analysis was carried out in order to identify the most important components of the algorithm and to properly tune the values of their parameters. The results of the computational experiments carried out show that this algorithm is very competitive in comparison to the best metaheuristic algorithms for the VRPB. Additionally, new best solutions have been found for two instances in one of the benchmark sets. Through these results, the paper shows that by expanding the exploration area and improving the efficiency of the local search heuristic, it is possible to develop simpler and faster metaheuristic algorithms without compromising the quality of the solutions obtained.
In this paper we present two algorithms, based on Greedy Randomized Adaptive Search Procedure and Tabu Search, for computing upper bounds for the forwarding index of a graph. A typical problem in the design of communication networks is determining how to interconnect each pair of nodes, without overloading any one of them. The forwarding index of a graph is a parameter that measures the load or congestion of the network seen as the number of interconnecting paths that pass through each node. The proposed algorithms have been tested on different sets of graphs for which theoretical values are known and also on randomly generated graphs of variable size and density. Experiments show that the algorithms find the optimal solution or a solution very close to the optimum in all cases. Our results are furthermore compared with the other heuristics for which computational results are available in the literature, showing that our algorithms behave as well as or better than these.
Abstract. Workflow Management Systems depend on a Workflow Enactment Service having several interfaces to establish communication with external applications, manage persistent information and exchange it with similarly capable systems. The study of business processes has shown multiple workflow patterns that have been modelled and implemented in several engines. The Workflow Management Council has combined commercial and academic efforts towards a standard structure for engines and information exchange regarding workflow processes.
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