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We address the one-to-one multi-commodity pickup and delivery traveling salesman problem (m-PDTSP) which is a generalization of the TSP and arises in several transportation and logistics applications. The objective is to find a minimum-cost directed Hamiltonian path which starts and ends at given depot nodes and such that the demand of each given commodity(More)
The rooted delay-constrained minimum spanning tree problem is an NP-hard combinatorial optimization problem arising for example in the design of centralized broadcasting networks where quality of service constraints are of concern. We present a construction heuristic based on Kruskal's algorithm for finding a minimum cost spanning tree which eliminates some(More)
The rooted delay-constrained minimum spanning tree problem is an NP-hard combinatorial optimization problem arising for example in the design of centralized broadcasting networks where quality of service constraints are of concern. We present two new approaches to solve this problem heuristically following the concepts of ant colony optimization (ACO) and(More)
We present a layered graph model for delay-constrained minimum tree problems with a polynomial number of constraints which can be solved well for instances with low-to medium-sized sets of achievable delay values and not too high bounds. Layered graph models have been recently shown to frequently yield tight bounds in the context of hop-or delay-constrained(More)
We consider the rooted delay-constrained Steiner tree problem which arises for example in the design of centralized multicasting networks where quality of service constraints are of concern. We present a mixed integer linear programming formulation based on the concept of feasible paths which has already been considered in the literature for the spanning(More)
This work deals with the application of metaheuristics to the fuel consumption minimization problem of hybrid electric vehicles (HEV) considering exactly specified driving cycles. A genetic algorithm, a downhill-simplex method and an algorithm based on swarm intelligence are used to find appropriate parameter values aiming at fuel consumption minimization.(More)
The rooted delay-constrained minimum spanning tree problem is an NP-hard combinatorial optimization problem. The problem appears in practice for example when designing a distribution network with a guarantee of timely delivery. Another example is be a centralized broadcasting network where the delaybound represents a quality of service constraint. We(More)
We present a memetic algorithm for a combinatorial optimization problem called rooted delay-constrained minimum spanning tree problem arising for example in centralized broadcasting networks where quality of service constraints are of concern. The memetic algorithm is based on a specialized solution representation and a simple and effective decoding(More)
A Video-on-Demand system usually consists of a large number of independent video servers. In order to utilize network resources as efficiently as possible the overall network load should be balanced among the available servers. We consider a problem formulation based on an estimation of the expected number of requests per movie during the period of highest(More)