A taxonomy of best-reply multifunctions in 2×2×2 trimatrix games

This paper provides an overview of the various shapes the best-reply multifunctions can take in 2×2×2 trimatrix games. It is shown that, unlike in 2×2 bimatrix games, the best replies to the opponents’ pure strategies do not completely determine the structure of the Nash equilibrium set.      

Existence and comparison results for fixed points of multifunctions with applications to normal-form games

In this paper we apply generalized iteration methods to prove comparison results which show how fixed points of a multifunction can be bounded by least and greatest fixed points of single-valued functions. As an application we prove existence and comparison results for fixed points of multifunctions. These results are applied to normal-form games, by proving existence and comparison results for pure and mixed Nash equilibria and their utilities.     

On the saddle-point stability for a class of dynamic games

In this paper, we study the stability properties of the class of capital accumulation games introduced by Fershtman and Muller (Ref. 1). Both discrete and continuous time versions are discussed. It is shown that the open-loop Nash equilibrium solutions for both games are characterized by a general saddle-point property, a result best known from the turnpike literature in optimal growth theory. In the case of zero discount rates, an even stronger result can be derived: As long as the Hessian matrix of the instantaneous profit functions has a quasidominant diagonal, no pure imaginary roots are possible.The authors thank J. Boyd III, G. Feichtinger, S. Jørgensen, and G. Schwann for helpful comments. The first author acknowledges financial support from the Natural Science and Engineering Research Council of Canada, Grant No. OGP-0037342.     

A BSDE approach to Nash equilibrium payoffs for stochastic differential games with nonlinear cost functionals

In this paper, we study Nash equilibrium payoffs for two-player nonzero-sum stochastic differential games via the theory of backward stochastic differential equations. We obtain an existence theorem and a characterization theorem of Nash equilibrium payoffs for two-player nonzero-sum stochastic differential games with nonlinear cost functionals defined with the help of doubly controlled backward stochastic differential equations. Our results extend former ones by Buckdahn et al. (2004) [3] and are based on a backward stochastic differential equation approach.     

On the existence of almost-pure-strategy Nash equilibrium in <Emphasis Type="Italic">n</Emphasis>-person finite games

This paper gives wide characterization of n-person non-coalitional games with finite players’ strategy spaces and payoff functions having some concavity or convexity properties. The characterization is done in terms of the existence of two-point-strategy Nash equilibria, that is equilibria consisting only of mixed strategies with supports being one or two-point sets of players’ pure strategy spaces. The structure of such simple equilibria is discussed in different cases. The results obtained in the paper can be seen as a discrete counterpart of Glicksberg’s theorem and other known results about the existence of pure (or “almost pure”) Nash equilibria in continuous concave (convex) games with compact convex spaces of players’ pure strategies.     

Computing the cores of strategic games with punishment–dominance relations

In this paper, we discuss the computational complexity of the strategic cores of a class of n-person games defined by Masuzawa (Int J Game Theory 32:479–483, 2003), which includes economic situations with monotone externality. We propose an algorithm for finding an α-core strategy of any game in this class which, counting the evaluation of a payoff for a strategy profile as one step, terminates after O(n ³· M) operations, where M is the maximum size of a strategy set of any of the n players. The idea underlying this method is based on the property of reduced games. This paper is based on a part of the doctoral dissertation of the author. The author thanks Mikio Nakayama, Masashi Umezawa, William Thomson, an associate editor, and the anonymous referee for their helpful comments, suggestions, and advice. Thanks are also due to Yukihiko Funaki for a comment that led the author to this subject. The author is responsible for errors and inadvertencies.     

Local stability of the Cournot solution with increasing heterogeneous competitors

In this paper we try to solve a paradox related to the results of Theocharis (1960). When the number of competitors increases the Cournot–Nash equilibrium loses stability. We relax the assumption about homogeneity in the decision mechanism and show that if we admit heterogeneity than by increasing the number of competitors the stability region on the parameters’ space may enlarge instead of shrinking.     

Bounding the inefficiency of Nash equilibria in games with finitely many players

This paper derives bounds on the gap between optimal performance and the performance of Nash equilibria in n-person games with continuous action sets. Specific interesting expressions are obtained for the average efficiency per player in congestion games.     

A class of differential games for which the closed-loop and open-loop Nash equilibria coincide

It is well known that, in general, Nash equilibria in open-loop strategies do not coincide with those in closed-loop strategies. This note identifies a class of differential games in which the Nash equilibrium in closed-loop strategies is degenerate, in the sense that it depends on time only. Consequently, the closed-loop equilibrium is also an equilibrium in open-loop strategies.The helpful comments of Professors Y. C. Ho, G. Leitmann, H. Y. Wan, Jr., and an anonymous referee are gratefully acknowledged.     

On the stability of the solution for multiobjective generalized games with the payoffs perturbed

This paper studies the stability of weakly Pareto-Nash and Pareto-Nash equilibrium for multiobjective generalized games with the payoff perturbed. Using a simple characterization of the weakly Pareto-Nash solution, we obtain a generic continuous result concerning weakly Pareto-Nash solution mapping. Examples are given to show that Pareto-Nash equilibrium mapping is neither upper semicontinuous nor lower semicontinuous. Through seeking the sub-mapping, we prove that most multiobjective generalized games have at least one essential Pareto-Nash solution.     

A capacity reservation game for suppliers with multiple blocks of capacity

This paper studies a supplier competition model in which a buyer reserves capacity from a number of suppliers that each have multiple blocks of capacity (e.g., production or power plants). The suppliers each submit a bid that specifies a reservation price and an execution price for every block, and the buyer determines what blocks to reserve. This game involves both external competition between suppliers and internal competition between blocks from each supplier. We characterize the properties of pure-strategy Nash equilibria for the game. Such equilibria may not always exist, and we provide the conditions under which they do.     

Common resources, optimality and taxes in dynamic games with increasing number of players

In the paper we examine the problem of exploitation of a common renewable resource. We use two kinds of models of this problem: games with finitely many players and games with a continuum of players. Equilibria in both cases are calculated and the payoffs are compared with payoffs in the situation in which each player behaves as a single owner of the resource. Various concepts of optimality are considered: optimality in the sense of property, Pareto optimality, maximization of a social welfare function of specific type and environmental sustainability. Another issue is the problem of enforcement of assumed profiles by so-called “linear” tax systems. Special attention is paid to the comparison of games with finitely many players and their continuum-of-players limit game.     

Computing the smallest fixed point of order-preserving nonexpansive mappings arising in positive stochastic games and static analysis of programs

The problem of computing the smallest fixed point of an order-preserving map arises in the study of zero-sum positive stochastic games. It also arises in static analysis of programs by abstract interpretation. In this context, the discount rate may be negative. We characterize the minimality of a fixed point in terms of the nonlinear spectral radius of a certain semidifferential. We apply this characterization to design a policy iteration algorithm, which applies to the case of finite state and action spaces. The algorithm returns a locally minimal fixed point, which turns out to be globally minimal when the discount rate is nonnegative.     

指派问题的多重最优解的择优方法

在某些情况下,经典指派问题的最优解不唯一．不同的最优解对参与人的影响不同,导致每个参与人会争取最有利于自身的最优解．为解决这个问题,通过研究允许合作指派问题的合作对策解的形成,提出允许合作指派问题的讨价还价模型和个体理性激励函数．在此基础上,提出了一个考虑个体理性的指派问题多重最优解的择优方法,从而保证了指派问题最优解的唯一性．     

A topological characterization of the existence of fixed points and applications

We prove a topological two‐way characterization of the existence of fixed‐points, without using linear or convexity structures and provide applications in optimization‐related problems. Such a characterization is also demonstrated for a fixed‐component point, a slight generalization of a fixed point.     

A hybrid extragradient method for approximating the common solutions of a variational inequality, a system of variational inequalities, a mixed equilibrium problem and a fixed point problem

In this paper, we give a hybrid extragradient iterative method for finding the approximate element of the common set of solutions of a generalized equilibrium problem, a system of variational inequality problems, a variational inequality problem and a fixed point problem for a strictly pseudocontractive mapping in a real Hilbert space. Further we establish a strong convergence theorem based on this method. The results presented in this paper improves and generalizes the results given in Yao et al. [36] and Ceng et al. [7], and some known corresponding results in the literature.