1,720,961 research outputs found
Coarse correlated equilibria for continuous time mean field games in open loop strategies
Get PDFIn the framework of continuous time symmetric stochastic differential games in open loop strategies, we introduce a generalization of mean field game solution, called coarse correlated solution. This can be seen as the analogue of a coarse correlated equilibrium in the N-player game. We justify our definition by showing that a coarse correlated solution for the mean field game induces a sequence of approximate coarse correlated equilibria with vanishing error for the underlying N-player games. Existence of coarse correlated solutions for the mean field game is proved by a minimax theorem. An example with explicit solutions is discussed as well
COARSE CORRELATED EQUILIBRIA IN CONTINUOUS-TIME MEAN FIELD GAMES
Get PDFMean field games (MFGs), an active theme of research since the mid 2000's, arise as the limit formulation of symmetric N-player games with mean field interactions, and they act as a treatable approximation of such games, when the numbers of players is large enough. The usual notion of MFG solution can be regarded as the infinitely many players counterpart of the concept of Nash equilibrium in the underlying N-player game, and the connection between Nash equilibria and solutions to the MFG can be made rigorous via convergence arguments.
The goal of this thesis is to introduce more general equilibria with better properties in continuous-time MFGs. In game theory literature, coarse correlated equilibria (CCEs) have been proposed as an alternative to Nash equilibria. CCEs can be seen as generalizations of the Nash equilibrium concept, incorporating a correlation device that allows agents to adopt correlated strategies without requiring cooperation. CCEs generalize Aumann's concept of correlated equilibria as well as Nash equilibria in both pure and mixed strategies. Among the nice features of CCEs, they are shown to be able to lead to higher payoffs than Nash equilibria in standard game theory, to be computationally ``easier'' and more natural to be learned by the players.
In this thesis, we introduce CCEs in continuous-time MFGs and study their properties. In each chapter a different framework is considered and different problems are addressed, each requiring specific methodologies. In particular, the first chapter presents abstract results on the existence of CCEs in MFGs and on the approximation of CCEs in the underlying N-player games by means of the former ones. Subsequent chapters focus on detailed studies of specific MFG models, in which it is possible to analytically compute CCEs (or at least some of them) and compare them with more classical solution concepts.
In Chapter 1 we consider MFGs driven by additive Wiener noise, with general drift and cost functions. The interaction term is given by a flow of probability measures, which appears both in the drift and in the cost functions. We introduce CCEs in both continuous time stochastic differential games and MFGs. The notion of coarse correlated solution to the MFG is justified by proving an approximation result. An existence result is also presented, whose proof relies on a minimax theorem.
In Chapter 2 we consider linear-quadratic MFGs. The interaction term is given by a flow of first order moments, which appears in the payoff functional only. A methodology to compute CCEs in such class of MFGs is provided and, through the study of a simple yet important example with applications in environmental economics, we show that there exist infinitely many CCEs for the MFG which both yield higher payoffs than the classical MFG solutions and are more efficient with respect to the environmental goals. Moreover, we provide instances of MFGs that do not admit any MFG solution, whereas infinitely many CCEs exist.
In Chapter 3 we consider a simple class of stationary MFGs of singular control. The reward, of ergodic type, is given by the long-time average of an expected utility functional. The interaction term is given by the stationary mean of the distribution of the representative player, which appears only in the reward. We provide constructive existence results, as well as approximation results and comparison with both MFG solutions and mean field control solutions. Finally, we show that CCEs may exist even when MFG solutions do not
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
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
Cooperation, correlation and competition in ergodic N-player games and mean-field games of singular controls: A case study
No full textWe consider ergodic symmetric N-player and mean-field games of singular control in both cooperative and competitive settings. The state process dynamics of a representative player follow geometric Brownian motion, controlled additively through a nondecreasing process. Agents aim to maximize a long-time average reward functional with instantaneous profit of power type. The game shows strategic complementarities, in that the marginal profit function is increasing with respect to the dynamic average of the states of the other players, when N < É, or with respect to the stationary mean of the players' distribution, in the mean-field case. In the mean-field formulation, we explicitly construct the solution to the mean-field control problem associated with central planner optimization, as well as Nash and coarse correlated equilibria (with singular and regular recommendations). Among our findings, we show that coarse correlated equilibria may exist even when Nash equilibria do not. Additionally, we show that a coarse correlated equilibrium with a regular (absolutely continuous) recommendation can outperform a Nash equilibrium where the equilibrium policy is of reflecting type (thus singularly continuous). Furthermore, we prove that the constructed mean-field control and mean-field equilibria can approximate the cooperative and competitive equilibria, respectively, in the corresponding game with N players when N is sufficiently large. To the best of our knowledge, this paper is the first to characterize coarse correlated equilibria, construct the explicit solution to an ergodic mean-field control problem, and provide approximation results for the related N -player game in the context of singular control games
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
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