1,720,986 research outputs found
Barrier trees for studying search landscapes
No full textThis thesis presents Barrier Trees and Barrier based models as tools to study small instances of problems exempla of the difficult problems faced by practitioners. Barrier Trees represent a cost landscape as a tree structure, with the leaves representing local minima and the internal nodes representing barriers between different parts of the landscape. They are a development of similar structures used in the study of protein folding, molecular clusters and potential energy surfaces amongst other fields. A novel definition of Barrier Trees is developed which has the advantage of defining a partitioning of the landscape, which can be used for further analysis and the animation of search heuristics working on the landscape. These techniques and various analyses using this partitioning are demonstrated. Barrier based models are model problems derived from small instances of real problems. They maintain the structure and connectivity between different local minima, and many other properties of the original problem, while massively reducing the state space. They provide a model Neighbourhood function that allows many different search algorithms to be implemented on the model problem, and they are particularly well suited to modelling search heuristics as Markov chains. These models are defined, and simple descent is used as an example of how the models can be used. The relationship between descent on the model problem and on the original problems is examined in detail. Variations on the basic model are explored.</p
Large Barrier Trees for Studying Search
No full textBarrier trees are a method for representing the landscape structure of high-dimensional discrete spaces such as those that occur in the cost function of combinatorial optimization problems. The leaves of the tree represent local optima and a vertex where subtrees join represents the lowest cost saddle-point between the local optima in the subtrees. This paper introduces an extension to existing Barrier tree methods that make them more useful for studying heuristic optimization algorithms. It is shown that every configuration in the search space can be mapped onto a vertex in the Barrier tree. This provides additional information about the landscape, such as the number of configurations in a local optimum. It also allows the computation of additional statistics such as the correlation between configurations in different parts of the Barrier tree. Furthermore, the mappings allow the dynamic behavior of a heuristic search algorithms to be visualized. This extension is illustrated using an instance of the MAX-3-SAT problem
Optimal parameters for search using a barrier tree Markov model
No full textAbstractThe performance, on a given problem, of search heuristics such as simulated annealing and descent with variable mutation can be described as a function of, and optimised over, the parameters of the heuristic (e.g. the annealing or mutation schedule). We describe heuristics as Markov processes; the search for optimal parameters is then rendered feasible by the use of level-accessible barrier trees for state amalgamation. Results are presented for schedules minimising “where-you-are” and “best-so-far” cost, over binary perceptron, spin-glass and Max-SAT problems. We also compute first-passage time for several “toy heuristics”, including constant-temperature annealing and fixed-rate mutation search
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
Evaluation of skill force
No full textThe evaluation considered the impact of Skill Force on pupil attendance, exclusions (fixed term and permanent), behaviour, and attainment. It also considered the factors which contributed towards the success of Skill Force, challenges for the future and value for money. Data were collected from a range of sources. Skill Force students and staff completed a questionnaire as did link teachers in schools and members of schools’ Senior Management Teams. Interviews were undertaken during visits to six projects. Data were collected from schools regarding attendance, exclusions and examination results.Overall, Skill Force is an extremely well managed programme which provides a unique service to schools. It has been successful in meeting the needs of many disaffected students,improving their motivation, confidence, communication and social skills. It has reduced exclusions, improved behaviour, attendance, attitudes towards education and attainment andalso provided students with a range of practical, vocational qualifications. It also offers excellent value for money
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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