1,721,059 research outputs found
Worst-Case Analysis of the Subset Sum Algorithm for Bin Packing
No full textWe analyze the worst-case ratio of a natural heuristic for the bin packing problem, which proceeds by filling one bin at a time, each as much as possible. A known lower bound on the worst-case ratio of this heuristic is 1.6067..., conjectured to be tight. In this paper, we show a nontrivial upper bound of 4/3 + ln (4/3) = 1.6210..., thus determining the value of the worst-case ratio within a relative error smaller than 1%. We also discuss how the lower and upper bounds extend to the case in which the maximum item size is bounded
An Effective Peak Period Heuristic for Railway Rolling Stock Planning
No full textIn this work we tackle a real-world application of railway rolling stock planning, known as the train unit assignment problem (TUAP), arising for a regional train operator in the North of Italy. Given a set of timetabled train trips, each with a demand of passenger seats, as well as a set of train units, each with a cost and a number of available passenger seats, the goal is to determine the minimum cost daily assignment of the train units to the trips, satisfying a set of operational constraints. The context we focus on is that of a competitive bid process whereby a train operator competes to win a contract for providing rolling stock circulation in a regional railway network. From a theoretical perspective, we prove that even a relaxation of the TUAP is NP-hard. To solve the TUAP, we propose a heuristic algorithm based on the optimal solution of the restricted problem associated with a peak period (i.e., a period of the day in which many trips overlapping in time must be performed). The heuristic algorithm is tested on real-world instances provided by the regional train operator and on larger realistic instances of TUAP. The obtained results are compared with those of previously developed methods, showing the effectiveness of the new algorithm that finds optimal or near-optimal solutions and outperforms, for what concerns both the solution quality and the computing time, the considered methods from the literature
Frontmatter, Table of Contents, Preface, Workshop Organization
No full textFrontmatter, Table of contents, Preface, Workshop Organizatio
Theoretical and computational results about optimality-based domain reductions
No full textIn this paper we discuss optimality-based domain reductions for Global Optimization problems both from the theoretical and from the computational point of view. When applying an optimality-based domain reduction we can easily define a lower limit for the reduction which can be attained, but we can hardly guarantee that such limit is reached. Here, we theoretically prove that, for a nontrivial class of problems, appropriate strategies exist that are always able to reach this lower limit. On the other hand, we will also show that the same strategies lose this property as soon as we slightly enlarge the class of problems. Next, we perform computational experiments with a standard B&B approach applied to Linear Multiplicative Programming problems. We aim at establishing a good trade off between the quality of the domain reduction (the higher the quality, the lower the number of nodes in the B&B tree), and the computational cost of the domain reduction, and, thus, the effort per node of the B&B tree
Delay-robust event scheduling
No full textRobust optimisation is a well-established concept to deal with uncertainty. In particular, recovery-robust models are suitable for real-world contexts, where a certain amount of recovery—although limited—is often available. In this paper we describe a general framework to optimise event-based problems against delay propagation. We also present a real-world application to train platforming in the Italian railways in order to show the practical effectiveness of our framework
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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