1,720,965 research outputs found
Forbidden Vertices for some classes of 0 - 1 polytopes
No full textThe forbidden-vertices problem aims to optimize a linear function over the vertices of a polytope that remains after prohibiting a given subset of them. We present extended formulations for this problem for some classes of 0 −1 polytopes. The sizes of the formulations are smaller than the known bounds for these polytopes.
We also compare this formulation on the Prize collecting TSP with other approaches that describe the same integer set, but generate different polytopes
New heuristics for the Max-Cut problem
No full textMax-Cut (or, equivalently, Quadratic Unconstrained Binary Optimization (QUBO))
is one of the most relevant and studied combinatorial optimization problems. In the
last decade, it got even more popularity after some innovative hardware, implementing heuristics that are based on quantum annealing, have been commercialized. These sys-
tems (QPU) are not general-purpose computers; as a matter of fact, they are able only to provide good solutions to QUBO instances defined on Chimera graphs, but in amazingly short computing times. The availability of such systems propelled a great deal of research focused on transforming real-world optimization problems (machine learning among the
many) to QUBO instances. The impact of the new technology became so strong that a QPU gained the cover page of TIME magazine in 2014.
A speedup factor of thousands or even a million times of QPU over some classical heuristics has been reported in the scientific literature. In contrast, Selby proposes a heuristic that provides more accurate solutions than QPU in not much longer times. The
heuristic is based on the so-called sub-graph sampling method. Essentially, the algorithm identifies a series of induced sub-graphs where Max-Cut is efficiently solvable due to their peculiar structure. Then the final solution is built from the solutions found on these sub-graphs. A recent study has shown that the Selby heuristic outperforms QPU both for solution quality and computing times. However, recently announced new versions of QPU can handle instances on graphs more complex than Chimera, whose tree-width is substantially higher, making Selby’s algorithm no longer applicable.
This fact motivates this paper where, sticking to the same sub-graph sampling method,
some structures of the induced sub-graphs, other than the tree-width, are exploited.
In particular, two structures are considered: outer-planarity and the sign of the edge-weights, possibly after applying operations like subset contraction and switching that are
commonly used in Max-Cut algorithms. The second structure makes it possible to apply the algorithm to any graph and not only to graphs with small tree-width like is the case for the algorithm of Selby.
We tested the algorithm on toroidal grid graphs, on the Chimera graphs used in the mentioned study
and on other instances in the literature obtaining encouraging results. For instance, we
are able to find the optimal solution for 94.42% of the 1355 Chimera instances in less than 1.72 seconds when using 560 simultaneous threads. Also, running the algorithm with 560 different seeds per instance, we observed that the optimum is attained at least once every
20 repetitions
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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