Coalition Formation and Potential Games

In this paper we study the formation of coalition structures in situations described by a cooperative game. Players choose independently which coalition they want to join. The payoffs to the players are determined by an allocation rule on the underlying game and the coalition structure that results from the strategies of the players according to some formation rule. We study two well-known coalition structure formation rules. We show that for both formation rules there exists a unique component efficient allocation rule that results in a potential game and study the coalition structures resulting from potential maximizing strategy profiles.cooperative game;coalition formation;potential game;potential maximizer

Coalition Formation and Potential Games

In this paper we study the formation of coalition structures in situations described by a cooperative game. Players choose independently which coalition they want to join. The payoffs to the players are determined by an allocation rule on the underlying game and the coalition structure that results from the strategies of the players according to some formation rule. We study two well-known coalition structure formation rules. We show that for both formation rules there exists a unique component efficient allocation rule that results in a potential game and study the coalition structures resulting from potential maximizing strategy profiles.

Potential Maximization and Coalition Government Formation

A model of coalition government formation is presented in which inefficient, non-minimal winning coalitions may form in Nash equilibrium. Predictions for five games are presented and tested experimentally. The experimental data support potential maximization as a refinement of Nash equilibrium. In particular, the data support the prediction that non-minimal winning coalitions occur when the distance between policy positions of the parties is small relative to the value of forming the government. These conditions hold in games 1, 3, 4 and 5, where subjects played their unique potential-maximizing strategies 91, 52, 82 and 84 percent of the time, respectively. In the remaining game (Game 2) experimental data support the prediction of a minimal winning coalition. Players A and B played their unique potential-maximizing strategies 84 and 86 percent of the time, respectively, and the predicted minimal-winning government formed 92 percent of the time (all strategy choices for player C conform with potential maximization in Game 2). In Games 1, 2, 4 and 5 over 98 percent of the observed Nash equilibrium outcomes were those predicted by potential maximization. Other solution concepts including iterated elimination of dominated strategies and strong/coalition proof Nash equilibrium are also tested.Coalition formation, Potential maximization, Nash equilibrium refinements, Experimental study, Minimal winning

Dynamic Coalition Formation and the Core

This paper presents a dynamic model of endogenous coalition formation in cooperative games with transferable utility. The players are boundedly rational. At each time step, a player decides which of the existing coalitions to join, and demands a payoff. These decisions are determined by a (non- cooperative) best-reply rule, given the coalition structure and allocation in the previous period. We show that absorbing states of the process exist if the game is essential. Further, if the players are allowed to experiment with myopically suboptimal strategies whenever there are potential gains from trade, an isomorphism between the set of absorbing states of the process and the set of core allocations can beestablished, and the process converges to one of these states with probability one whenever the core is non-empty. This result holds independently of the form of the characteristic function.TU Games; Coalition Formation; Bounded Rationality; Core

Mechanism Design for Team Formation

Team formation is a core problem in AI. Remarkably, little prior work has addressed the problem of mechanism design for team formation, accounting for the need to elicit agents' preferences over potential teammates. Coalition formation in the related hedonic games has received much attention, but only from the perspective of coalition stability, with little emphasis on the mechanism design objectives of true preference elicitation, social welfare, and equity. We present the first formal mechanism design framework for team formation, building on recent combinatorial matching market design literature. We exhibit four mechanisms for this problem, two novel, two simple extensions of known mechanisms from other domains. Two of these (one new, one known) have desirable theoretical properties. However, we use extensive experiments to show our second novel mechanism, despite having no theoretical guarantees, empirically achieves good incentive compatibility, welfare, and fairness.Comment: 12 page

Why is the Doha development agenda failing? And what can be done?: A computable general equilibrium-game theoretical approach

"We herein use a world Computable General Equilibrium (CGE) model to simulate 143 potential trade reforms and seek solutions to the issues hampering progress in the Doha Development Agenda (DDA). Inside the domain defined by all these possible outcomes, we apply the axiomatic theory of bargaining and select the Nash solution of cooperative games. The solutions vary according to the objective functions adopted by the trade negotiators. When real income is the objective and services are excluded, or when optimizing terms of trade is the objective, the Nash solution is the status quo. Trade liberalization is feasible only when the negotiators focus on national exports or Gross Domestic Product (GDP). Our assessment of some possible solutions reveals that excluding members having a GDP below a certain threshold improves the bargaining process, regardless of the governments' objective. Formation of coalition, such as the G20, constitutes an option for its members to block outcomes imposed by rich members. We also find that side payments may be a solution, but represent a very high share of the global income gain." from authors' abstractTrade negotiations, Computable general equilibrium (CGE) modeling, Nash solution, Side payments, Cooperative games, Globalization, Markets, Doha Development Agenda,

Stochastic Coalitional Better-response Dynamics and Strong Nash Equilibrium

We consider coalition formation among players in an n-player finite strategic game over infinite horizon. At each time a randomly formed coalition makes a joint deviation from a current action profile such that at new action profile all players from the coalition are strictly benefited. Such deviations define a coalitional better-response (CBR) dynamics that is in general stochastic. The CBR dynamics either converges to a strong Nash equilibrium or stucks in a closed cycle. We also assume that at each time a selected coalition makes mistake in deviation with small probability that add mutations (perturbations) into CBR dynamics. We prove that all strong Nash equilibria and closed cycles are stochastically stable, i.e., they are selected by perturbed CBR dynamics as mutations vanish. Similar statement holds for strict strong Nash equilibrium. We apply CBR dynamics to the network formation games and we prove that all strongly stable networks and closed cycles are stochastically stable

Coalition Formation Game for Cooperative Cognitive Radio Using Gibbs Sampling

This paper considers a cognitive radio network in which each secondary user selects a primary user to assist in order to get a chance of accessing the primary user channel. Thus, each group of secondary users assisting the same primary user forms a coaltion. Within each coalition, sequential relaying is employed, and a relay ordering algorithm is used to make use of the relays in an efficient manner. It is required then to find the optimal sets of secondary users assisting each primary user such that the sum of their rates is maximized. The problem is formulated as a coalition formation game, and a Gibbs Sampling based algorithm is used to find the optimal coalition structure.Comment: 7 pages, 2 figure

Dynamic club formation with coordination

We present a dynamic model of jurisdiction formation in a society of identical people. The process is described by a Markov chain that is defined by myopic optimization on the part of the players. We show that the process will converge to a Nash equilibrium club structure. Next, we allow for coordination between members of the same club,i.e. club members can form coalitions for one period and deviate jointly. We define a Nash club equilibrium (NCE) as a strategy configuration that is immune to such coalitional deviations. We show that, if one exists, this modified process will converge to a NCE configuration with probability one. Finally, we deal with the case where a NCE fails to exist due to indivisibility problems. When the population size is not an integer multiple of the optimal club size, there will be left over players who prevent the process from settling down. We define the concept of an approximate Nash club equilibrium (ANCE), which means that all but k players are playing a Nash club equilibrium, where k is defined by the minimal number of left over players. We show that the modified process converges to an ergodic set of states each of which is ANCE