Search results for "Heuristic"
showing 10 items of 476 documents
GRASP for the uncapacitated r-allocation p-hub median problem
2014
In this paper we propose a heuristic for the Uncapacitated r-Allocation p-Hub Median Problem. In the classical p-hub location problem, given a set of nodes with pairwise traffic demands, we must select p of them as hub locations and route all traffics through them at a minimum cost. We target here an extension, called the r-allocation p-hub median problem, recently proposed by Yaman [19], in which every node is assigned to r of the p selected hubs (r@?p) and we are restricted to route the traffic of the nodes through their associated r hubs. As it is usual in this type of problems, our method has three phases: location, assignment and routing. Specifically, we propose a heuristic based on t…
A double genetic algorithm for the MRCPSP/max
2011
This paper presents a heuristic solution procedure for a very general resource-constrained project scheduling problem. Here, multiple execution modes are available for the individual activities of the project. In addition, minimum as well as maximum time lags between different activities may be given. The objective is to determine a mode and a start time for each activity such that the temporal and resource constraints are met and the project duration is minimised. Project scheduling problems of this type occur e.g. in process industries. The heuristic is a two-phased genetic algorithm with different representation, fitness, crossover operator, etc., in each of them. One of the contribution…
Active-guided evolution strategies for large-scale capacitated vehicle routing problems
2007
We present an adaptation of the active-guided evolution strategies metaheuristic for the capacitated vehicle routing problem. The capacitated vehicle routing problem is a classical problem in operations research in which a set of minimum total cost routes must be determined for a fleet of identical capacitated vehicles in order to service a number of demand or supply points. The applied metaheuristic combines the strengths of the well-known guided local search and evolution strategies metaheuristics into an iterative two-stage procedure. The computational experiments were carried out on a set of 76 benchmark problems. The results demonstrate that the suggested method is highly competitive, …
GRASP and path relinking for the equitable dispersion problem
2013
The equitable dispersion problem consists in selecting a subset of elements from a given set in such a way that a measure of dispersion is maximized. In particular, we target the Max-Mean dispersion model in which the average distance between the selected elements is maximized. We first review previous methods and mathematical formulations for this and related dispersion problems and then propose a GRASP with a Path Relinking in which the local search is based on the Variable Neighborhood methodology. Our method is specially suited for instances in which the distances represent affinity and are not restricted to take non-negative values. The computational experience with 120 instances shows…
Variable neighborhood search for the linear ordering problem
2006
Given a matrix of weights, the linear ordering problem (LOP) consists of finding a permutation of the columns and rows in order to maximize the sum of the weights in the upper triangle. This NP-complete problem can also be formulated in terms of graphs, as finding an acyclic tournament with a maximal sum of arc weights in a complete weighted graph. In this paper, we first review the previous methods for the LOP and then propose a heuristic algorithm based on the variable neighborhood search (VNS) methodology. The method combines different neighborhoods for an efficient exploration of the search space. We explore different search strategies and propose a hybrid method in which the VNS is cou…
An Aggressive Search Procedure for the Bipartite Drawing Problem
1996
Graphs are used to represent reality in several areas of knowledge. This has generated considerable interest in graph drawing algorithms. Arc crossing minimization is a fundamental aesthetic criterion to obtain a readable map of a graph. The problem of minimizing the number of arc crossings in a bipartite graph (BDP) is NP-complete. In this paper we present an aggressive search scheme for the BDP based on the Intensification, Diversification and Strategic Oscillation elements of Tabu Search. Several algorithms can be obtained with this scheme by implementing different evaluators in the move definitions. In this paper we propose two variants. Computational results are reported on a set of 30…
Reference Priors in a Variance Components Problem
1992
The ordered group reference prior algorithm of Berger and Bernardo (1989b) is applied to the balanced variance components problem. Besides the intrinsic interest of developing good noninformative priors for the variance components problem, a number of theoretically interesting issues arise in application of the proposed procedure. The algorithm is described (for completeness) in an important special case, with a detailed heuristic motivation.
Most Diverse Near-Shortest Paths
2021
Computing the shortest path in a road network is a fundamental problem that has attracted lots of attention. However, in many real-world scenarios, determining solely the shortest path is not enough as users want to have additional, alternative ways of reaching their destination. In this paper, we investigate a novel variant of alternative routing, termed the k-Most Diverse Near-Shortest Paths (kMDNSP). In contrast to previous work, kMDNSP aims at maximizing the diversity of the recommended paths, while bounding their length based on a user-defined constraint. Our theoretical analysis proves the NP-hardness of the problem at hand. To compute an exact solution to kMDNSP, we present an algori…
A Multistart Scatter Search Heuristic for Smooth NLP and MINLP Problems
2005
The algorithm described here, called OptQuest/NLP or OQNLP, is a heuristic designed to find global optima for pure and mixed integer nonlinear problems with many constraints and variables, where all problem functions are differentiable with respect to the continuous variables. It uses OptQuest, a commercial implementation of scatter search developed by OptTek Systems, Inc., to provide starting points for a gradient-based local NLP solver. This solver seeks a local solution from a subset of these points, holding discrete variables fixed. The procedure is motivated by our desire to combine the superior accuracy and feasibility-seeking behavior of gradient-based local NLP solvers with the glob…
Optimal Delay-Power Tradeoff in Sparse Delay Tolerant Networks: a preliminary study
2006
In this paper we present a first attempt to study analytically the tradeoff between delivery delay and resource consumption for epidemic routing in Delay Tolerant Networks. We assume that the nodes cooperate in order to minimize a common cost equal to a weighted sum of the packet delivery delay and the total number of copies, which is strongly related to the power consumption. In this framework we determine the best policy each node should deploy in a very simple scenario where all the nodes have perfect knowledge of the system status. The result is used as an ideal reference to evaluate the performance of some heuristics proposed, investigating potential performance improvements and config…