1,720,959 research outputs found
A Column Generation Approach for Pure Parsimony Haplotyping
No full textWe present two integer programming models for the Haplotype Inference by Pure Parsimony problem. The first model uses variables to decide the haplotype coordinates and the two haplotypes that explain each genotype, and contains quadratic constraints. By decomposition, we obtain a second linear model where all the possible haplotypes and genotype subsets are enumerated and each variable decides if a haplotype explains a genotype subset. Preliminary tests show that the linear relaxation, solved by column generation, is tight and often provides the optimal integer solution for small instances
Bilevel programming and price setting problems
No full textThis paper is devoted to pricing optimization problems which can be modeled as bilevel programs. We present the main concepts, models and solution methods for this class of optimization problems.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
A Polyhedral Study for Delay Management in Public Transportation
No full textThe attractiveness of intermodal public transportation networks is strongly related to the reliability of connections between vehicles. As a consequence, operational decisions are required to manage connections in case of unpredictable events like breakdowns or vehicle delays. In such cases, the network operators have to determine if connected vehicles should wait for the delayed ones or keep their schedule. The Delay Management Problem (DMP) consists in defining a wait/depart policy that minimizes the total delay incurred by passengers. In this work we present a polyhedral study for DMP: starting from a previous integer linear programming formulation and from results on the Mixed 0-1 Knapsack Polytope, we derive new valid inequalities and we show that they define facets of the convex-hull of some special cases
Stochastic Assignment with Gammit Path Choice Models
No full textTraffic assignment models simulate transportation systems, where flows resulting from user choice behaviour are affected by transportation costs, and costs may be affected by flows due to congestion. Several path choice behaviour models can be specified through random utility theory. Probabilistic path choice models, where perceived path costs are modelled as random variables, lead to stochastic assignment. In this paper, reasonable modelling requirements are proposed to assure a realistic simulation of path choice behaviour through probabilistic choice models. Then, additive Gammit path choice models based on Gamma distribution are introduced and deeply analysed. These models satisfy all the proposed modelling requirements, and can be effectively embedded within existing models and algorithms for stochastic assignment
Data analytics for trajectory selection and preference-model extrapolation in the European airspace
Full text linkRepresenting airspace users’ preferences in Air Traffic Flow Management (ATFM) mathematical models is becoming of high relevance. ATFM models aim to reduce congestion (en-route and at both departure and destination airports) and maximize the Air Traffic Management (ATM) system efficiency by determining the best trajectory for each aircraft. In this framework, the a-priori selection of possible alternative trajectories for each flight plays a crucial role. In this work, we analyze initial trajectories queried from Eurocontrol DDR2 data source. Clustering trajectories yields groups that are homogeneous with respect to known (geometry of the trajectory, speed) and partially known or unknown factors (en-route charges, fuel consumption, weather, etc.). Associations between grouped trajectories and potential choice-determinants are successively explored and evaluated, and the predictive value of the determinants is finally validated. For a given origin-destination pair, this ultimately leads to determining a set of flight trajectories and information on related airspace users’ preferences
An Improved Arcflow Model for the Skiving Stock Problem
Full text linkBecause of the sharp development of (commercial) MILP software and hardware components, pseudo-polynomial formulations have been established as a viable tool for solving cutting and packing problems in recent years. Constituting a natural (but independent) counterpart of the well-known cutting stock problem, the one-dimensional skiving stock problem (SSP) asks for the maximal number of large objects (specified by some threshold length) that can be obtained by recomposing a given inventory of smaller items. In this paper, we introduce a new arcflow formulation for the SSP applying the idea of reflected arcs. In particular, this new model is shown to possess significantly fewer variables as well as a better numerical performance compared to the standard arcflow formulation
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
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