1,720,978 research outputs found
The Complexity of Simulation and Matrix Multiplication
No full textComputing the simulation preorder of a given Kripke structure (i.e., a directed graph with n labeled vertices) has crucial applications in model checking of temporal logic. It amounts to solving a specific two-players reachability game, called simulation game. We offer the first conditional lower bounds for this problem, and we relate its complexity (for computation, verification, and certification) to some variants of n × n matrix multiplication. We show that any O(na)-time algorithm for simulation games, even restricting to acyclic games/structures, can be used to compute n χ n boolean matrix multiplication (BMM) in O(nα) time. In the acyclic case, we match this bound by presenting the first subcubic algorithm, based on fast BMM, and running in nω +°(1) time (where ω < 2.376 is the exponent of matrix multiplication). For both acyclic and cyclic structures, we point out the existence of natural and canonical O(n2)-size certificates, that can be verified in truly subcubic time by means of matrix multiplication. In the acyclic case, O(n2) time is sufficient, employing standard (+, ×)-matrix product verification. In the cyclic case, a min-edge witness matrix multiplication (EWMM) is used, i.e., a matrix multiplication on the semi-ring (max, ×) where one matrix contains only 0's and 1's, which is computable in truly subcubic n(3+ω)/2+o(1) time. Finally, we show a reduction from EWMM to cyclic simulation games which implies a separation between the cyclic and the acyclic cases, unless EWMM can be verified in nω+°(1) time. Read More: http://epubs.siam.org/doi/10.1137/1.9781611974782.14
Dynamic Controllability of Conditional Simple Temporal Networks Is PSPACE-complete
No full textEven after the proposal of various solution algorithms, the precise computational complexity of checking whether a Conditional Temporal Network is Dynamically Controllable had still remained widely open. This issue gets settled in this paper which provides constructions, algorithms, and bridging lemmas and arguments to formally prove that: (1) the problem is PSPACE-hard, and (2) the problem lies in PSPACE
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
New Bounds for Approximating Extremal Distances in Undirected Graphs
No full textIn this thesis, we consider the problem of computing approximations of extremal distances in undirected graphs, namely the diameter, the radius and the eccentricity of every vertex. This is a basic problem in computational graph theory: a number of recent results attracted the interest of researchers. We present some of the algorithmic techniques recently discovered to address this problem and the conditional lower bounds on its complexity, with particular focus on the relation with combinatorial and graph-theoretic aspects.
This thesis includes some results obtained by the author in collaboration with professor Roberto Grossi (thesis advisor, University of Pisa) and professor Romeo Rizzi (University of Verona), including new algorithms, conditional impossibility results, and combinatorial insights that improve our understanding of the problem. Our original contributions resulted in a paper which will be presented at the conference ACM--SIAM Symposium on Discrete Algorithms (SODA) in January 2016
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