Existence of pure Nash equilibria in discontinuous and non quasiconcave games

In a recent but well known paper, Reny has proved the existence of Nash equilibria for compact and quasiconcave games, with possibly discontinuous payoff functions. In this paper, we prove that the quasiconcavity assumption in Reny’s theorem can be weakened: we introduce a measure allowing to localize the lack of quasiconcavity, which allows to refine the analysis of equilibrium existence (I wish to thank P. J. Reny, two anonymous referees and the associated editor for corrections, suggestions and remarks which led to improvements in the paper).     

The Compromise Value for Cooperative Games with Random Payoffs

This paper introduces and studies the compromise value for cooperative games with random payoffs, that is, for cooperative games where the payoff to a coalition of players is a random variable. This value is a compromise between utopia payoffs and minimal rights and its definition is based on the compromise value for NTU games and the τ-value for TU games. It is shown that the nonempty core of a cooperative game with random payoffs is bounded by the utopia payoffs and the minimal rights. Consequently, for such games the compromise value exists. Further, we show that the compromise value of a cooperative game with random payoffs coincides with the τ-value of a related TU game if the players have a certain type of preferences. Finally, the compromise value and the marginal value, which is defined as the average of the marginal vectors, coincide on the class of two-person games. This results in a characterization of the compromise value for two-person games.I thank Peter Borm, Ruud Hendrickx and two anonymous referees for their valuable comments.     

The polarized Ramsey’s theorem

We study the effective and proof-theoretic content of the polarized Ramsey’s theorem, a variant of Ramsey’s theorem obtained by relaxing the definition of homogeneous set. Our investigation yields a new characterization of Ramsey’s theorem in all exponents, and produces several combinatorial principles which, modulo bounding for formulas, lie (possibly not strictly) between Ramsey’s theorem for pairs and the stable Ramsey’s theorem for pairs. We are grateful to D. Hirschfeldt, A. Montalbán, and R. Soare for making our collaboration possible and for helpful comments and suggestions. We thank J. Schmerl for first bringing the subject of polarized partitions to our attention and J. Mileti for his generous insights. We also thank one anonymous referee for valuable observations and corrections. The first author was partially supported by an NSF Graduate Research Fellowship.     

Globalization, social development, and operations research: an exploration of strategies for success

This paper argues that in today’s world order, policy-making takes precedence over analytical and technical models that have historically formed the mainstay of Operations Research. The structural and human dimensions of this transition is discussed in the form of six Policy Imperatives aimed at the creation of a world order that makes it more humane and less vulnerable to failure. It is proposed that though OR occupies a prominent role in developmental initiatives, in order for its successful implementation in meeting social goals, the context in which it is invoked must be conducive to social transformation. An earlier version of this paper was presented at the International Conference on Operations Research for Development (ICORD) held December 27–30, 2002 at Anna University, Chennai. The author would like to acknowledge the helpful comments of anonymous reviewers. He would also like to thank Professor K.S.P. Rao of Anna University for his gracious assistance.     

Less is more: an observability paradox in repeated games

We present a repeated prisoners’ dilemma game with imperfect public monitoring, which exhibits the following paradoxical feature: the (limit) equilibrium payoff set achieves full efficiency asymptotically as the public signal becomes insensitive to the hidden actions of the players. The basic logic behind this result also provides an example where the Folk theorem is obtained, while Fudenberg et al.’s (in Econometrica 62:997–1040, 1994) sufficient conditions for Folk theorem are violated.We would like to thank Drew Fudenberg, David Levine, an associate editor and two anonymous referees for their helpful comments and suggestions.     

On the relevance of alternatives in bargaining: generalized average pay-off solutions

We generalize the average pay-off solution proposed by Anbarci (Can J Econ 28:675–682, 1995), which depends on all the alternatives, and show that the Nash and Kalai–Smorodinsky solutions are limits of generalized average pay-off solutions. We formalize the notion of relevant alternatives and compare solutions in terms of the relevance of alternatives. I am much indebted to Roberto Serrano for his guidance and many discussions, and William Thomson for his numerous detailed suggestions for improvements. I thank Youngsub Chun, Michael Maschler, Yeneng Sun, Rajiv Vohra, Oscar Volij, Myrna Wooders, an associate editor, anonymous referees, and seminar participants at Brown University, the National University of Singapore, and the 2003 North American Summer Meetings of the Econometric Society for valuable comments. I gratefully acknowledge research support from Brown University through an Eccleston Fellowship award.     

Pricing Options on Defaultable Stocks*

? ?. This work was inspired by the SAMSI workshops on Financial Mathematics, Statistics and Econometrics (Fall 2005, Spring 2006 North Carolina). The author wishes to thank the organizers for the travel grant to participate in this stimulating event. I also would like to thank Bo Yang for his research assistance and the two anonymous referees and an anonymous associate editor for their valuable suggestions. Stock option price approximations are developed for a model which takes both the risk of default and the stochastic volatility into account. The intensity of defaults is assumed to be influenced by the volatility. It is shown that it might be possible to infer the risk neutral default intensity from the stock option prices. The proposed option price approximation has a rich implied volatility surface structure and fits the data implied volatility well. A calibration exercise shows that an effective hazard rate from bonds issued by a company can be used to explain the impliedvolatility skew of the option prices issued by the same company. It is also observed that the implied yield spread obtained from calibrating all the model parameters to the option prices matches the observed yield spread.     

Dinkelbach Approach to Solving a Class of Fractional Optimal Control Problems

We consider optimal control problems with functional given by the ratio of two integrals (fractional optimal control problems). In particular, we focus on a special case with affine integrands and linear dynamics with respect to state and control. Since the standard optimal control theory cannot be used directly to solve a problem of this kind, we apply Dinkelbach’s approach to linearize it. Indeed, the fractional optimal control problem can be transformed into an equivalent monoparametric family {P_q} of linear optimal control problems. The special structure of the class of problems considered allows solving the fractional problem either explicitly or requiring straightforward classical numerical techniques to solve a single equation. An application to advertising efficiency maximization is presented. This work was partially supported by the Università Ca’ Foscari, Venezia, Italy, the MIUR (PRIN cofinancing 2005), the Council for Grants (under RF President) and State Aid to Fundamental Science Schools (Grant NSh-4113.2008.6). We thank Angelo Miele, Panos Pardalos and the anonymous referees for comments and suggestions.     

On the incentive properties of multi-item auctions

In a market of indivisible objects where a buyer consumes at most one object, the buyer-optimal auction is a multi-item generalization of Vickrey's second-price auction. If the optimal auction is formulated as a strategic game, it is well-known that it satisfies good incentive properties, i.e., the honest strategy profile is a Nash equilibrium, a unique perfect equilibrium and a dominant strategy equilibrium. For each of the three incentive properties, it is shown that the optimal auction is aunique auction satisfying the property. The uniqueness results are derived in a general setting with budget constraints and non-linear utilities.I would like to thank three anonymous referees for detailed comments and constructive suggestions. I would also like to thank Edward J. Green and John G. Riley for their valuable comments and advice on earlier drafts of this paper. I am solely responsible for any errors.     

On equilibrium in pure strategies in games with many players

We demonstrate that, if there are sufficiently many players, any Bayesian equilibrium of an incomplete information game can be “ε-purified” . That is, close to any Bayesian equilibrium there is an approximate Bayesian equilibrium in pure strategies. Our main contribution is obtaining this result for games with a countable set of pure strategies. In order to do so we derive a mathematical result, in the spirit of the Shapley–Folkman Theorem, permitting countable strategy sets. Our main assumption is a “large game property,” dictating that the actions of relatively small subsets of players cannot have large affects on the payoffs of other players. E. Cartwright and M. Wooders are indebted to Phillip Reny, Frank Page and two anonymous referees for helpful comments.     

Negotiation,preferences over agreements,and the core

We analyze conditions under which negotiated agreements are efficient from the point of view of every possible coalition of negotiators. The negotiators have lexicographic preferences over agreements they reach. Their utility is the first criterion. The coalition reaching an agreement is the second criterion. In the analyzed non-cooperative discrete time bargaining game Γ the players bargain about the choice from the sets of utility vectors feasible for coalitions in a given NTU game (N, V). If Γ has a Markov perfect equilibrium, then the set of equilibrium utility vectors in Markov perfect equilibria in it equals the core of (N, V). I thank an anonymous referee, an anonymous Associate Editor, and the Editor for their comments that helped me to improve the paper. The research reported in this paper was supported by the Grant VEGA 1/1223/04 of the Ministry of Education of the Slovak Republic.     

Consistent values and the core in continuum market games with two types of players

The consistent value is an extension of the Shapley value to the class of games with non-transferable utility.? In this paper, the consistent value will be characterized for market games with a continuum of players of two types. We will show that for such games the consistent value need not belong to the core, and provide conditions under which there is equivalence between the two concepts. Received: October 1998 RID="*" ID="*"  This thesis was completed under the supervision of Professor Sergiu Hart, The Center for Rationality and Interactive Decision Theory, Department of Mathematics, Department of Economics, The Hebrew University of Jerusalem. I would like to thank Professor Hart for introducing me to this area of research, for his help and guidance, and, especially, for all his patience.? I would also like to thank Michael Borns for improving the style, and an anonymous referee for helpful comments.     

Periodic Solutions for a Class of Second-Order Ordinary Differential Equations

This paper is devoted to the study of periodic solutions for a class of second-order ordinary differential equations by utilizing a technique for obtaining solutions to free problems in the calculus of variations originating in the work of Carathéodory (Ref. 1, 1935). The key of this technique is to find some suitable transformation which transfers the periodic solution problem to an equivalent variational problem in which the minimizer is more easily determined. Some applications are presented to illustrate the utility of this technique.Supported by NSFC Grant 10401013, 985 Project of Jilin University and Graduate Innovation Lab of Jilin University. The authors thank Professor D. A. Carlson and the anonymous referees for valuable suggestions and helpful comments.     

A Discrete-Time Dynamic Game of Seasonal Water Allocation

We present a method for the derivation of feedback Nash equi- libria in discrete-time finite-horizon nonstationary dynamic games. A partic- ular motivation for such games stems from environmental economics, where problems of seasonal competition for water levels occur frequently among heterogeneous economic agents. These agents are coupled through a state variable, which is the water level. Actions are strategically chosen to max- imize the agents individual season-dependent utility functions. We observe that, although a feedback Nash equilibrium exists, it does not satisfy the (exogenous) environmental watchdog expectations. We devise an incentive scheme to help meeting those expectations and calculate a feedback Nash equilibrium for the new game that uses the scheme. This solution is more environmentally friendly than the previous one. The water allocation game solutions help us to draw some conclusions regarding the agents behavior and also about the existence of feedback Nash equilibria in dynamic games. The paper draws from Refs.1–2. Its earlier version was presented at the Victoria International Conference 2004, Victoria University of Wellington, Wellington, New Zealand, February 9–13, 2004. We thank the anonymous referee and Christophe Deissenberg for insightful comments, which have helped us to clarify its message. We also thank our colleagues Sophie Thoyer, Robert Lifran, Odile Pourtalier, and Vladimir Petkov for helpful discussions on the model and techniques used in this Paper. Gratitude is expressed to the Kyoto Institute for Economic Research, Kyoto University, for this author's support in the final stages of the paper preparation     

Pairwise-stability and Nash equilibria in network formation

Suppose that individual payoffs depend on the network connecting them. Consider the following simultaneous move game of network formation: players announce independently the links they wish to form, and links are formed only under mutual consent. We provide necessary and sufficient conditions on the network link marginal payoffs such that the set of pairwise stable, pairwise-Nash and proper equilibrium networks coincide, where pairwise stable networks are robust to one-link deviations, while pairwise-Nash networks are robust to one-link creation but multi-link severance. Under these conditions, proper equilibria in pure strategies are fully characterized by one-link deviation checks. We thank William Thomson, an associate editor and two anonymous referees for their suggestions that led to substantial improvements. We also thank Sjaak Hurkens, Bettina Klaus, Jordi Massó and Giovanni Neglia for helpful conversations. The first author gratefully acknowledges the financial support from the Spanish Ministry of Education and FEDER through grant SEJ2005-01481/ECON, the Fundación BBVA and the Barcelona Economics Program of XREA. The second author is grateful to the Netherlands Organization for Scientific Research (NWO) for its support under grant VIDI-452-06-013.     

Optimal Supply Functions in Electricity Markets with Option Contracts and Non-smooth Costs

In this paper we investigate the optimal supply function for a generator who sells electricity into a wholesale electricity spot market and whose profit function is not smooth. In previous work in this area, the generator’s profit function has usually been assumed to be continuously differentiable. However in some interesting instances, this assumption is not satisfied. These include the case when a generator signs a one-way hedge contract before bidding into the spot market, as well as a situation in which a generator owns several generation units with different marginal costs. To deal with the non-smooth problem, we use the model of Anderson and Philpott, in which the generator’s objective function is formulated as a Stieltjes integral of the generator’s profit function along his supply curve. We establish the form of the optimal supply function when there are one-way contracts and also when the marginal cost is piecewise smooth.We would like to thank two anonymous referees for careful reading of the paper and helpful comments which lead to a significant improvement of this paper.     

Multiplicative K-theory and K-theory of Functors

In this article we give a construction of Max Karoubi’s multiplicative K-theory as the K-theory of an appropriate functor between two categories. We use this construction to explain why the two definitions of relative multiplicative K-theory for a compact pair of manifolds we give in the article agree. Part of this work has been done while I was holding an EEC postdoctoral position funded by the network ‘Algebraic K-theory, linear algebraic groups and related structures’ at University College Dublin. I would like to thank Professor David Lewis for inviting me to Dublin. During the later stages of the work, I was supported by EPSERC grant GR/S08046/01.     

The money-burning refinement: With an application to a political signalling game

We define an equilibrium refinement in signalling games by allowing agents to refine the game by burning money whenever they can act. We apply the refinement in a model where the public is unsure about the ability of an agent, say a government, to foresee the effects of long-term decisions. A government with ample information about the consequences of decisions should invest either immediately or not at all. Poorly informed agents should wait for better information. We identify pooling equilibria in which excessive rush or waiting occurs. The money-burning refinement may eliminate both rash and waiting pooling equilibria, but it involves wasting money and, for high discount factors, a decrease in welfare.First version August 1997/This version March 2004For valuable suggestions and comments I would like to thank Hans-Jörg Beilharz, Eric van Damme, Ulrich Erlenmaier, Ami Glazer, Paul Grout, Volker Hahn, Hans Haller, Majia Halonen, Martin Hellwig, Verena Liessem, Till Requate, Gisèle Umbhauer, seminar participants in Bristol, Heidelberg and Mannheim and at the Conference of the European Public Choice Society 1998 in Goeteborg, two anonymous referees, and the associate editor.     

Optimal compensation with adverse selection and dynamic actions

We consider continuous-time models in which the agent is paid at the end of the time horizon by the principal, who does not know the agent’s type. The agent dynamically affects either the drift of the underlying output process, or its volatility. The principal’s problem reduces to a calculus of variation problem for the agent’s level of utility. The optimal ratio of marginal utilities is random, via dependence on the underlying output process. When the agent affects the drift only, in the risk- neutral case lower volatility corresponds to the more incentive optimal contract for the smaller range of agents who get rent above the reservation utility. If only the volatility is affected, the optimal contract is necessarily non-incentive, unlike in the first-best case. We also suggest a procedure for finding simple and reasonable contracts, which, however, are not necessarily optimal. Research supported in part by NSF grants DMS 04-03575 and 06-31298. We would like to express our gratitude to participants of the following seminars and conferences for useful comments and suggestions: UCLA (Econ Theory), Caltech (Econ Theory), Columbia (Probability), Princeton (Fin. Engineering), U. Texas at Austin (Math Finance), Banff Workshop on Optim. Problems in Fin. Econ, Kyoto U. (Economics), UC Irvine (Probability), Cornell (Fin. Engineering), Bachelier Seminar. Moreover, we are very grateful to the anonymous referee for helpful suggestions. The remaining errors are the authors’ sole responsibility.