1,721,056 research outputs found
Locating Facilities on a Network to Minimize Their Average Service Radius
No full textLet G = (V, E) denote an undirected weighted graph of n nodes and m edges, and let U ⊆ V. The relative eccentricity of a node u ∈ U is the maximum distance in G between u and any other node of U, while the radius of U in G is the minimum relative eccentricity of all the nodes in U. Several facility location problems ask for partitioning the nodes of G so as to minimize some global optimization function of the radii of the subsets of the partition. Here, we focus on the problem of partitioning the nodes of G into exactly p ≥ 2 non-empty subsets, so as to minimize the sum of the subset radii, called the total radius of the partition. This problem can be easily seen to be NP-hard when p is part of the input, but when p is fixed it can be solved in polynomial time by reducing it to a similar partitioning problem. In this paper, we first present an efficient O(n3) time algorithm for the notable case p = 2, which improves the O(mn2 + n3 log n) running time obtainable by applying the aforementioned reduction. Then, in an effort of characterizing meaningful polynomial-time solvable instances of the problem when p is part of the input, we show that (i) when G is a tree, then the problem can be solved in O(n3p3) time, and (ii) when G has bounded treewidth h, then the problem can be solved in O(n4h+4p3) time
Nearly Linear Time Minimum Spanning Tree Maintenance for Transient Node Failures
Get PDFGiven a 2-node connected, real weighted, and undirected graph G=(V,E), with n nodes and m edges, and given a minimum spanning tree (MST) T=(V,ET) of G, we study the problem of finding, for every node v in V, a set of replacement edges which can be used for constructing an MST of G-v (i.e., the graph G deprived of v and all its incident edges). We show that this problem can be solved on a pointer machine in O(m ·alpha(m,n)) time and O(m) space, where alpha() is the functional inverse of Ackermann’s function. Our solution improves over the previously best known O(min{m ·alpha(n,n), m + n logn}) time bound, and allows us to close the gap existing with the fastest solution for the edge-removal version of the problem (i.e., that of finding, for every edge e in ET, a replacement edge which can be used for constructing an MST of G-e=(V,E\{e}). Our algorithm finds immediate application in maintaining MST-based communication networks undergoing temporary node failures. Moreover, in a distributed environment in which nodes are managed by selfish agents, it can be used to design an efficient, truthful mechanism for building an MST
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Computational aspects of a 2-player Stackelberg shortest paths tree game
No full textLet a communication network be modelled by a directed graph G = (V,E) of n nodes and m edges. We consider a one-round two-player network pricing game, the Stackelberg Shortest Paths Tree (StackSPT) game. This is played on G, by assuming that edges in E are partitioned into two sets: a set E F of edges with a fixed positive real weight, and a set E P of edges that should be priced by one of the two players (the leader). Given a distinguished node r ∈ V, the StackSPT game is then as follows: the leader prices the edges in E P in such a way that he will maximize his revenue, knowing that the other player (the follower) will build a shortest paths tree of G rooted at r, say S(r), by running a publicly available algorithm. Quite naturally, for each edge selected in the solution, the leader’s revenue is assumed to be equal to the loaded price of an edge, namely the product of the edge price times the number of paths from r in S(r) that use it. First, we show that the problem of maximizing the leader’s revenue is NP-hard as soon as |E P | = Θ(n). Then, in search of an effective method for solving the problem when the size of E P is constant, we focus on the basic case in which |E P | = 2, and we provide an efficient O(n 2 logn) time algorithm. Afterwards, we generalize the approach to the case |E P | = k, and we show that it can be solved in polynomial time whenever k = O(1)
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Reoptimization of weighted graph and covering problems
No full textGiven an instance of an optimization problem and a good solution of that instance, the reoptimization is a concept of analyzing how does the solution change when the instance is locally modified. We investigate reoptimization of the following problems: Maximum Weighted Independent Set, Maximum Weighted Clique, Minimum Weighted Dominating Set, Minimum Weighted Set Cover and Minimum Weighted Vertex Cover. The local modifications we consider are addition or removal of a constant number of edges to the graph, or elements to the covering sets in case of Set Cover problem. We present the following results: 1 We provide a PTAS for reoptimization of the unweighted versions of the aforementioned problems when the input solution is optimal. 1 We provide two general techniques for analyzing approximation ratio of the weighted reoptimization problems. 1 We apply our techniques to reoptimization of the considered optimization problems and obtain tight approximation ratios in all the cases. © 2009 Springer Berlin Heidelberg
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