1,721,011 research outputs found
An Adaptive Iterated Local Search for the Mixed Capacitated General Routing Problem
Full text linkWe study the mixed capacitated general routing problem (MCGRP) in which a fleet of capacitated vehicles has to serve a set of requests by traversing a mixed weighted graph. The requests may be located on nodes, edges, and arcs. The problem has theoretical interest because it is a generalization of the capacitated vehicle routing problem (CVRP), the capacitated arc routing problem (CARP), and the general routing problem. It is also of great practical interest since it is often a more accurate model for real-world cases than its widely studied specializations, particularly for so-called street routing applications. Examples are urban waste collection, snow removal, and newspaper delivery. We propose a new iterated local search metaheuristic for the problem that also includes vital mechanisms from adaptive large neighborhood search combined with further intensification through local search. The method utilizes selected, tailored, and novel local search and large neighborhood search operators, as well as a new local search strategy. Computational experiments show that the proposed metaheuristic is highly effective on five published benchmarks for the MCGRP. The metaheuristic yields excellent results also on seven standard CARP data sets, and good results on four well-known CVRP benchmarks, including improvement of the best known upper bound for one instance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Stuck between a rock and a hard place - The pleasures of practicing OR in a contract research organization
Full text linkIn this talk I will share some personal experiences and thoughts. My career has followed an old-fashioned scheme. The contract research organization SINTEF has been my employer for more than 30 years. My normal defence is that I have changed roles and topics a few times. I have moved from CAD via AI to OR, also up and down the organization hierarchy. I will touch upon on the pleasures and hardships of being stuck between academia and industry. The main topic will be RTD on rich vehicle routing problems
A Hybrid Metaheuristic for a Multi-Objective Mixed Capaciated General Routing Problem
No full textIn this thesis, we have studied a bi-objective variant of the Mixed Capacitated General Routing Problem (MCGRP). The MCGRP is a generalization of other well known routing problems. It is defined on a mixed, weighted graph, where a homogeneous fleet of vehicles with capacity constraints services a set of required entities. These entities can be nodes, directed arcs and undirected edges. The aim of the problem is to find a set of vehicle routes so that every required entity is serviced exactly once and the total route cost is minimized. In the current work, a bi-objective variant of the MCGRP is proposed, where also route balance is optimized.
To solve the problem, a hybrid metaheuristic solution method is proposed. The aim of the method is to find a diversified set of Pareto optimal solutions with high quality objective values. The solution method is a variant of a genetic algorithm to obtain a diversified set of solutions, combined with local search based heuristics to improve the quality of the objective values.
This is the first study of multi-objective variants of the MCGRP, hence the results cannot be compared directly with results from other studies. Instead, the performance of the method is evaluated by visual inspection of the plotted Pareto front and by comparing the quality of the objective values with the best known solutions to the single-objective MCGRP.
The solution method is conducted on 23 instances. Solutions that are as good as the best known solutions of the single-objective MCGRP was found for two of them, of which one is known to be optimal. The solutions were well spread out along the Pareto front for most of the instances, but a large population size or multiple runs of the same instance is necessary to obtain a good approximation of the Pareto front. For most of the instances, the objectives are conflicting, meaning they cannot be simultaneously optimized.
There is still a lot of research potential for the multi-objective MCGRP, and we hope this thesis will motivate further research
Industrial Vehicle Routing
Full text linkSolving the Vehicle Routing Problem (VRP) is a key to efficiency in transportation and supply chain management. The VRP is a computationally hard problem that comes in many guises. The VRP literature contains thousands of papers, and VRP research is regarded as one of the great successes of OR. An industry of routing tool vendors has emerged. Exact optimization methods of today cannot consistently solve VRP instances with more than 50-100 customers in reasonable time, which is generally a small number in real-life applications. For industrial problem sizes, and if one aims at solving a variety of VRP applications, approximation methods is the only viable approach. In this talk, a brief motivation and introduction to the VRP will be given. We then describe how industrial requirements motivate extensions to the basic, rather idealized VRP models that have received most attention in the research community, and how such extensions can be made. At SINTEF, industrial variants of the VRP have been studied since 1995. Our efforts have led to the development of a generic VRP solver that has been commercialized through a spin-off company. As an illustration, a description of the underlying, rich VRP model and the selected uniform algorithmic approach, which is based on metaheuristics, is given. Examples of applications will be presented, along with results from computational experiments. There is still a need for VRP research to meet industrial requirements, particularly for large-scale instances and complex, rich VRP variants, for instance in the context of routing in combination of inventory management and fleet composition. Examples of ongoing projects will be given. In conclusion, we point to future trends and important issues in further VRP research.Industrial Vehicle Routin
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