On the Existence of Pure-Strategy Equilibria in Large Games

Over the years, several formalizations and existence results for games with a continuum of players have been given. These include those of Schmeidler (1973), Rashid (1983), Mas-Colell (1984), Khan and Sun (1999) and Podczeck (2007a). The level of generality of each of these existence results is typically regarded as a criterion to evaluate how appropriate is the corresponding formalization of large games. In contrast, we argue that such evaluation is pointless. In fact, we show that, in a precise sense, all the above existence results are equivalent. Thus, all of them are equally strong and therefore cannot rank the different formalizations of large games.

On the Existence of Pure Strategy Nash Equilibria in Large Games

We consider an asymptotic version of Mas-Colells theorem on the existence of pure strategy Nash equilibria in large games. Our result states that, if players payoff functions are selected from an equicontinuous family, then all sufficiently large games have an " pure, " equilibrium for all " > 0. We also show that our result is equivalent to Mas-Colells existence theorem, implying that it can properly be considered as its asymptotic version.

On the Existence of Pure Strategy Nash Equilibria in Large Games

We consider an asymptotic version of Mas-Colell's theorem on the existence of pure strategy Nash equilibria in large games. Our result states that, if players' payoff functions are selected from an equicontinuous family, then all sufficiently large games have an epsilon - pure, epsilon - equilibrium for all epsilon greater than 0. We also show that our result is equivalent to Mas-Colell's existence theorem, implying that it can properly be considered as its asymptotic version.Nash Equilibrium; Asymptotic Results; Pure Strategies; Approximate equilibria; Equicontinuity; Purification

On the Existence of Pure Strategy Nash Equilibria in Large Games

Over the years, several formalizations of games with a continuum of players have been given. These include those of Schmeidler (1973), Mas-Colell (1984) and Khan and Sun (1999). Unlike the others, Khan and Sun (1999) also addressed the equilibrium problem of large ¯- nite games, establishing the existence of a pure strategy approximate equilibrium in su±ciently large games. This ability for their formal- ization to yield asymptotic results led them to argue for it as the right approach to games with a continuum of players. We challenge this view by establishing an equivalent asymptotic theorem based only on Mas-Colell's formalization. Furthermore, we show that it is equivalent to Mas-Colell's existence theorem. Thus, in contrast to Khan and Sun (1999), we conclude that Mas-Colell's for- malization is as good as theirs for the development of the equilibrium theory of large ¯nite games.

On the existence of pure-strategy equilibria in large games

Over the years, several formalizations and existence results for games with a continuum of players have been given. These include those of Schmeidler (1973), Rashid (1983), Mas-Colell (1984), Khan and Sun (1999) and Podczeck (2007a). The level of generality of each of these existence results is typically regarded as a criterion to evaluate how appropriate is the corresponding formalization of large games. In contrast, we argue that such evaluation is pointless. In fact, we show that, in a precise sense, all the above existence results are equivalent. Thus, all of them are equally strong and therefore cannot rank the different formalizations of large games

On the Existence of Pure Strategy Nash Equilibria in Large Games

We consider an asymptotic version of Mas-Colell’s theorem on the existence of pure strategy Nash equilibria in large games. Our result states that, if players’ payoff functions are selected from an equicontinuous family, then all sufficiently large games have an ε – pure, ε – equilibrium for all ε > 0. We also show that our result is equivalent to Mas-Colell’s existence theorem, implying that it can properly be considered as its asymptotic version.N/

On the existence of pure strategy equilibria in large generalized games with atomic players

We consider a game with a continuum of players where only a finite number of them are atomic. Objective functions and admissible strategies may depend on the actions chosen by atomic players and on aggregate information about the actions chosen by non-atomic players. Only atomic players are required to have convex sets of admissible strategies and quasi-concave objective functions. We prove the existence of a pure strategy Nash equilibria. Thus, we extend to large generalized games with atomic players the results of equilibrium existence for non-atomic games of Schemeidler (1973) and Rath (1992). We do not obtain a pure strategy equilibrium by purification of mixed strategy equilibria. Thus, we have a direct proof of both Balder (1999, Theorem 2.1) and Balder (2002, Theorem 2.2.1), for the case where non-atomic players have a common non-empty set of strategies and integrable bounded codification of action profiles. Our main result is readily applicable to many interesting problems in general equilibrium. As an application, we extend Aumann (1966) result on the existence of equilibrium with a continuum of traders to a standard general equilibrium model with incomplete asset markets.Generalized games; Non-convexities; Pure-strategy Nash equilibrium

Three essays on bounded rationality and individual learning in repeated games

This thesis is composed of three chapters, which can be read independentlyIn the first chapter, we revisit the El Farol bar problem developed by Brian W. Arthur (1994) to investigate how one might best model bounded rationality in economics. We begin by modelling the El Farol bar problem as a market entry game and describing its Nash equilibria. Then, assuming agents are boundedly rational in accordance with a reinforcement learning model, we analyse long-run behaviour in the repeated game. We then state our main result. In a single population of individuals playing the El Farol game, reinforcement learning predicts that the population is eventually subdivided into two distinct groups: those who invariably go to the bar and those who almost never do. In doing so we demonstrate that reinforcement learning predicts sorting in the El Farol bar problem.The second chapter considers the long-run behaviour of agents learning in finite population games with random matching. In particular we study finite population games composed of anti-coordination pair games. We find the set of conditions for the payoff matrix of the two-player pair game that ensures the existence of strict pure strategy equilibria in the finite population game. Furthermore, we suggest that if the population is sufficiently large and the two-player pair games meet certain criteria, then the long-run behaviour of individuals, learning in accordance with the Erev and Roth (1998) reinforcement model, asymptotically converges to pure strategy profiles of the population game. These are equilibria where all individual agents play pure strategies, while in aggregate the frequencies of pure strategies played in the population mimic the mixed strategy equilibrium in the pair game. In addition we gather further evidence through computer simulations.The third chapter investigates some of the theoretical predictions of learning theory in anti-coordination finite population games with random matching through laboratory experiments in economics. Previous data from experiments on anticoordination games has focused on aggregate behaviour and has evidenced that outcomes mimic the mixed strategy equilibrium. Here we show that in finite population anti-coordination games, reinforcement learning predicts sorting; that is, in the long-run, agents play pure strategy equilibria where subsets of the population permanently play each available action

Stochastic dominance equilibria in two-person noncooperative games

Two-person noncooperative games with finitely many pure strategies and ordinal preferences over pure outcomes are considered, in which probability distributions resulting from mixed strategies are evaluated according to t-degree stochastic dominance. A t-best reply is a strategy that induces a t-degree stochastically undominated distribution, and a t-equilibrium is a pair of t-best replies. The paper provides a characterization and existence proofs of t-equilibria in terms of representing utility functions, and shows that for t becoming large-which can be interpreted as the players becoming more risk averse-behavior converges to a specific form of max-min play. More precisely, this means that in the limit each player puts all weight on a strategy that maximizes the worst outcome for the opponent, within the supports of the strategies in the limiting sequenceof t-equilibria.microeconomics ;

On the existence of pure strategy equilibria in large generalized games with atomic players

We consider a game with a continuum of players where only a finite number of them are atomic. Objective functions and admissible strategies may depend on the actions chosen by atomic players and on aggregate information about the actions chosen by non-atomic players. Only atomic players are required to have convex sets of admissible strategies and quasi-concave objective functions. We prove the existence of a pure strategy Nash equilibria. Thus, we extend to large generalized games with atomic players the results of equilibrium existence for non-atomic games of Schemeidler (1973) and Rath (1992). We do not obtain a pure strategy equilibrium by purification of mixed strategy equilibria. Thus, we have a direct proof of both Balder (1999, Theorem 2.1) and Balder (2002, Theorem 2.2.1), for the case where non-atomic players have a common non-empty set of strategies and integrable bounded codification of action profiles. Our main result is readily applicable to many interesting problems in general equilibrium. As an application, we extend Aumann (1966) result on the existence of equilibrium with a continuum of traders to a standard general equilibrium model with incomplete asset markets