1,720,962 research outputs found
Games with congestion-averse utilities
No full textCongestion games—in which players strategically choose from a set of “resources” and derive utilities that depend on the congestion on each resource— are important in a wide range of applications. However, to date, such games have been constrained to use utility functions that are linear sums with respect to resources. To remove this restriction, this paper provides a significant generalisation to the case where a player’s payoff can be given by any real-valued function over the set of possible congestion vectors. Under reasonable assumptions on the structure of player strategy spaces, we constructively prove the existence of a pure strategy equilibrium for the very wide class of these generalised games in which player utility functions are congestion-averse—i.e., monotonic, submodular and independent of irrelevant alternatives. Although, as we show, these games do not admit a generalised ordinal potential function (and hence—the finite improvement property), any such game does possess a Nash equilibrium in pure strategies. A polynomial time algorithm for computing such an equilibrium is presented
Optimal strategies for bidding agents participating in simultaneous Vickrey auctions with perfect substitutes
Full text linkWe derive optimal strategies for a bidding agent that participates in multiple, simultaneous second-price auctions with perfect substitutes. We prove that, if everyone else bids locally in a single auction, the global bidder should always place non-zero bids in all available auctions, provided there are no budget constraints. With a budget, however, the optimal strategy is to bid locally if this budget is equal or less than the valuation. Furthermore, for a wide range of valuation distributions, we prove that the problem of finding the optimal bids reduces to two dimensions if all auctions are identical. Finally, we address markets with both sequential and simultaneous auctions, non-identical auctions, and the allocative efficiency of the market
Approximating Mixed Nash Equilibria using Smooth Fictitious Play in Simultaneous Auctions
No full textWe investigate equilibrium strategies for bidding agents that participate in multiple, simultaneous second-price auctions with perfect substitutes. For this setting, previous research has shown that it is a best response for a bidder to participate in as many such auctions as there are available, provided that other bidders only participate in a single auction. In contrast, in this paper we consider equilibrium behaviour where all bidders participate in multiple auctions. For this new setting we consider mixed-strategy Nash equilibria where bidders can bid high in one auction and low in all others. By discretising the bid space, we are able to use smooth fictitious play to compute approximate solutions. Specifically, we find that the results do indeed converge to -Nash mixed equilibria and, therefore, we are able to locate equilibrium strategies in such complex games where no known solutions previously existed
On the Impact of Strategy and Utility Structures on Congestion-Averse Games
No full textRecent results regarding games with congestion-averse utilities (or, congestion-averse games---CAGs) have shown they possess some very desirable properties. Specifically, they have pure strategy Nash equilibria, which may be found by a polynomial time algorithm. However, these results were accompanied by a very limiting assumption that each player is capable of using any subset of its available set of resources. This is often unrealistic---for example, resources may have complementarities between them such that a minimal number of resources is required for any to be useful. To remove this restriction, in this paper we prove the existence and tractability of a pure strategy equilibrium for a much more general setting where each player is given a matroid over the set of resources, along with the (upper and lower) bounds on the size of a subset of resources to be selected, and its strategy space consists of all elements of this matroid that fit in the given size range. (This, in particular, includes the possibility of having a full matroid, or having a set of bases of a matroid.) Moreover, we show that if a player strategy space in a given CAG does not satisfy these matroid properties, then a pure strategy equilibrium need not exist, and in fact the determination of whether or not a game has a pure strategy Nash equilibrium is NP-complete. We further prove analogous results for each of the congestion-averse conditions on utility functions, thus showing that current assumptions on strategy and utility structures in this model cannot be relaxed anymore
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
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