Anytime Coalition Structure Generation with Worst Case Guarantees

Coalition formation is a key topic in multiagent systems. One would prefer a coalition structure that maximizes the sum of the values of the coalitions, but often the number of coalition structures is too large to allow exhaustive search for the optimal one. But then, can the coalition structure found via a partial search be guaranteed to be within a bound from optimum? We show that none of the previous coalition structure generation algorithms can establish any bound because they search fewer nodes than a threshold that we show necessary for establishing a bound. We present an algorithm that establishes a tight bound within this minimal amount of search, and show that any other algorithm would have to search strictly more. The fraction of nodes needed to be searched approaches zero as the number of agents grows. If additional time remains, our anytime algorithm searches further, and establishes a progressively lower tight bound. Surprisingly, just searching one more node drops the bound in half. As desired, our algorithm lowers the bound rapidly early on, and exhibits diminishing returns to computation. It also drastically outperforms its obvious contenders. Finally, we show how to distribute the desired search across self-interested manipulative agents

Complexity of Determining Nonemptiness of the Core

Coalition formation is a key problem in automated negotiation among self-interested agents, and other multiagent applications. A coalition of agents can sometimes accomplish things that the individual agents cannot, or can do things more efficiently. However, motivating the agents to abide to a solution requires careful analysis: only some of the solutions are stable in the sense that no group of agents is motivated to break off and form a new coalition. This constraint has been studied extensively in cooperative game theory. However, the computational questions around this constraint have received less attention. When it comes to coalition formation among software agents (that represent real-world parties), these questions become increasingly explicit. In this paper we define a concise general representation for games in characteristic form that relies on superadditivity, and show that it allows for efficient checking of whether a given outcome is in the core. We then show that determining whether the core is nonempty is $\mathcal{NP}$-complete both with and without transferable utility. We demonstrate that what makes the problem hard in both cases is determining the collaborative possibilities (the set of outcomes possible for the grand coalition), by showing that if these are given, the problem becomes tractable in both cases. However, we then demonstrate that for a hybrid version of the problem, where utility transfer is possible only within the grand coalition, the problem remains $\mathcal{NP}$-complete even when the collaborative possibilities are given

Naïve Learning in Social Networks: Convergence, Influence and Wisdom of Crowds

We study learning and influence in a setting where agents communicate according to an arbitrary social network and naïvely update their beliefs by repeatedly taking weighted averages of their neighbors’ opinions. A focus is on conditions under which beliefs of all agents in large societies converge to the truth, despite their naïve updating. We show that this happens if and only if the influence of the most influential agent in the society is vanishing as the society grows. Using simple examples, we identify two main obstructions which can prevent this. By ruling out these obstructions, we provide general structural conditions on the social network that are sufficient for convergence to truth. In addition, we show how social influence changes when some agents redistribute their trust, and we provide a complete characterization of the social networks for which there is a convergence of beliefs. Finally, we survey some recent structural results on the speed of convergence and relate these to issues of segregation, polarization and propaganda.Social Networks, Learning, Diffusion, Bounded Rationality

Can Reforms be Made Sustainable?: Analysis and Design Considerations for the Electricity Sector

This document discusses and proposes a new framework to improve the quality of programs supporting such reforms in Latin America. Firstly, it responds to the risk that the reforms in the region might be reversed, which might originate in the lack of public support for privatization and the succession of crises and events in the recent past (problems of supply in Chile and Brazil; price peaks in the spot market in El Salvador; the commercial unsustainability of the pool in Colombia; the ENRON/Andersen scandal, and the Argentine crisis among others), that have provided the enemies of reform with new political space. Secondly, it responds to evidence that the consolidation of sector reforms is not automatic, involving as it does the simultaneous creation of traditions of respect for the rights of investors and consumers. Finally, this paper partly builds upon the experience gathered from a project supporting the sustainability of electricity reform in Colombia, Guatemala and Honduras.Urban Development, Energy & Mining, electrcity sector, sustainable design, privatization, electricity reform

Investment Under Uncertainty, Market Evolution and Coalition Spillovers in a Game Theoretic Perspective.

The rationality assumption has been the center of neo-classical economics for more than half a century now. In recent years much research has focussed on models of bounded rationality. In this thesis it is argued that both full and bounded rationality can be used for different kind of problems. In the first part full rationality is assumed to analyse technology adoption by firms in a duopolistic and uncertain environment. In the second part, boundedly rational models are developed to study the evolution of market structure in oligopolistic markets as well as price formation on (possibly) incomplete financial markets. The third part of the thesis presents an alternative to the framework of Transferable Utility games in cooperative game theory. The model introduced here explicitly takes into account the outside options that players often have in real-life situations if they choose not to participate in a coalition.

Public Choice, Constitutional Political Economy and Law and Economics

The various subdisciplines within the emerging ‘new institutionalism’ in economics all draw special attention to the legal-political constraints within which economic and political agents choose and therefore represent a return of economics to its appropriate legal foundations. By changing the name of his research program to constitutional political economy Buchanan distanced himself from those parts of the public choice literature that remained too close to the traditional welfare economics approach. This chapter draws lessons for law and economics from recent developments in the re-emerging field of constitutional political economy. CPE compares alternative sets of institutional arrangements, in markets and the polity, and their outcomes, using ‘democratic consent’ as an internal standard of comparison. The chapter discusses the methodological foundation of the CPE approach, presents Buchanan’s reconstruction of the Coase theorem along subjectivist-contractarian lines and gives an overview of recent contributions to the literature. JEL classification: B41, D70, H10, K; Keywords: Constitutional Economics, Constitutional Political Economy, Public Choice, James M. Buchanan, Methodological FoundationLaw and Economics, Constitutional Economics

Theorizing EU trade politics

This special issue aims to take the first step towards an inter-paradigmatic debate in the study of European Union trade politics

Learning in evolutionary environments

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