1,720,974 research outputs found
The price of anarchy of affine congestion games with similar strategies
Full text linkAffine congestion games are a well-studied model for selfish behavior in distributed systems, such as transportation and communication networks. Seminal influential papers in Algorithmic Game Theory have bounded the worst-case inefficiency of Nash equilibria, termed as price of anarchy, in several variants of these games. In this work, we investigate to what extent these bounds depend on the similarities among the players' strategies. Our notion of similarity is modeled by assuming that, given a parameter θ ≥ 1, the costs of any two strategies available to a same player, when evaluated in absence of congestion, are within a factor θ one from the other. It turns out that, for the non-atomic case, better bounds can always be obtained for any finite value of θ. For the atomic case, instead, θ < 3/2 and θ < 2 are necessary and sufficient conditions to obtain better bounds in games played on general graph topologies and on parallel link graphs, respectively. It is worth noticing that small values of θ model the behavioral attitude of players who are partially oblivious to congestion and are not willing to significantly deviate from what is their best strategy in absence of congestio
Uniform Mixed Equilibria in Network Congestion Games with Link Failures
No full textMotivated by possible applications in fault-tolerant selfish routing, we introduce the notion of uniform mixed equilibrium in network congestion games with adversarial link failures, where agents need to route traffic from a source to a destination node. Given an integer p >_ 1, a p-uniform mixed strategy is a mixed strategy in which an agent plays exactly p edge-disjoint paths with uniform probability; therefore, a p-uniform mixed equilibrium is a tuple of p-uniform mixed strategies, one for each agent, in which no agent can lower her cost by deviating to another p-uniform mixed strategy. For games with weighted agents and affine latency functions, we show the existence of p-uniform mixed equilibria and provide a tight characterization of their price of anarchy. For games with unweighted agents, we extend the existential guarantee to any class of latency functions, and restricted to games with affine latencies, we derive a tight characterization of the price of anarchy and the price of stability
On Stackelberg Strategies in Affine Congestion Games
No full textWe investigate the efficiency of some Stackelberg strategies in congestion games with affine latency functions. A Stackelberg strategy is an algorithm that chooses a subset of players and assigns them a prescribed strategy with the purpose of mitigating the detrimental effect that the selfish behavior of the remaining uncoordinated players may cause to the overall performance of the system. The efficiency of a Stackelberg strategy is measured in terms of the price of anarchy of the pure Nash equilibria they induce. Three Stackelberg strategies, namely Largest Latency First, Cover and Scale, were already considered in the literature and non-tight upper and lower bounds on their price of anarchy were given. We reconsider these strategies and provide the exact bound on the price of anarchy of both Largest Latency First and Cover and a better upper bound on the price of anarchy of Scale
Dynamic taxes for polynomial congestion games
No full textWe consider the efficiency of taxation in congestion games with polynomial latency functions along the line of research initiated by Caragiannis et al. [ACM Transactions on Algorithms, 2010], who focused on both pure and mixed Nash equilibria in games with affine latencies only. By exploiting the primal-dual method [Bilò, Proceedings of the 10th Workshop on Approximation and Online Algorithms, 2012], we obtain interesting upper bounds with respect to a variety of different solution concepts ranging from approximate pure Nash equilibria up to approximate coarse correlated equilibria, and including also approximate one-round walks starting from the empty state. Our findings show a high beneficial effect of taxation that increases more than linearly with the degree of the latency functions. In some cases, a tight relationship with some well-studied polynomials in Combinatorics and Number Theory, such as the Touchard and the Geometric polynomials, arises. In these cases, we can also show matching lower bounds, albeit under mild assumptions; interestingly, our upper bounds are derived by exploiting the combinatorial definition of these polynomials, while our lower bounds are constructed by relying on their analytical characterization
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
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