Default risk in an interconnected banking system with endogeneous asset markets : [Version: August 2011]

This paper analyzes the emergence of systemic risk in a network model of interconnected bank balance sheets. Given a shock to asset values of one or several banks, systemic risk in the form of multiple bank defaults depends on the strength of balance sheets and asset market liquidity. The price of bank assets on the secondary market is endogenous in the model, thereby relating funding liquidity to expected solvency - an important stylized fact of banking crises. Based on the concept of a system value at risk, Shapley values are used to define the systemic risk charge levied upon individual banks. Using a parallelized simulated annealing algorithm the properties of an optimal charge are derived. Among other things we find that there is not necessarily a correspondence between a bank's contribution to systemic risk - which determines its risk charge - and the capital that is optimally injected into it to make the financial system more resilient to systemic risk. The analysis has policy implications for the design of optimal bank levies. JEL Classification: G01, G18, G33 Keywords: Systemic Risk, Systemic Risk Charge, Systemic Risk Fund, Macroprudential Supervision, Shapley Value, Financial Networ

Shapley Value Based Multi-Agent Reinforcement Learning: Theory, Method and Its Application to Energy Network

Multi-agent reinforcement learning is an area of rapid advancement in artificial intelligence and machine learning. One of the important questions to be answered is how to conduct credit assignment in a multi-agent system. There have been many schemes designed to conduct credit assignment by multi-agent reinforcement learning algorithms. Although these credit assignment schemes have been proved useful in improving the performance of multi-agent reinforcement learning, most of them are designed heuristically without a rigorous theoretic basis and therefore infeasible to understand how agents cooperate. In this thesis, we aim at investigating the foundation of credit assignment in multi-agent reinforcement learning via cooperative game theory. We first extend a game model called convex game and a payoff distribution scheme called Shapley value in cooperative game theory to Markov decision process, named as Markov convex game and Markov Shapley value respectively. We represent a global reward game as a Markov convex game under the grand coalition. As a result, Markov Shapley value can be reasonably used as a credit assignment scheme in the global reward game. Markov Shapley value possesses the following virtues: (i) efficiency; (ii) identifiability of dummy agents; (iii) reflecting the contribution and (iv) symmetry, which form the fair credit assignment. Based on Markov Shapley value, we propose three multi-agent reinforcement learning algorithms called SHAQ, SQDDPG and SMFPPO. Furthermore, we extend Markov convex game to partial observability to deal with the partially observable problems, named as partially observable Markov convex game. In application, we evaluate SQDDPG and SMFPPO on the real-world problem in energy networks.Comment: 206 page

A Survey of Models of Network Formation: Stability and Efficiency

I survey the recent literature on the formation of networks. I provide definitions of network games, a number of examples of models from the literature, and discuss some of what is known about the (in)compatibility of overall societal welfare with individual incentives to form and sever links

Strategic Resource Dependence

We consider a situation where an exhaustible-resource seller faces demand from a buyer who has a perfect substitute but there is a time-to-build delay for the substitute. We that find in this simple framework the basic implications of the Hotelling model (1931) are reversed: over time the stock declines but supplies increase up to the point where the buyer decides to switch. Under such a threat of demand change, the supply does not reflect the true current resource scarcity but leads to increased future scarcity, felt during the transition to the substitute supplies. The analysis suggests a perspective on costs of oil dependence.Dynamic Bilateral Monopoly, Markov-Perfect Equilibrium, Depletable Resources, Energy, Alternative Fuels, Oil Dependence

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.

Why Mergers Reduce Profits and Raise Share Prices: A Theory of Preemptive Mergers

We explain the empirical puzzle why mergers reduce profits and raise share prices. If being an "insider" is better than being an "outsider," firms may merge to preempt their partner merging with a rival. The stock-value of the insiders is increased, since the risk of becoming an outsider is eliminated. We also explain why shareholders of targets gain while acquirers typically break even. These results are derived in an endogenousmerger model, predicting the conditions under which mergers occur, when they occur, and how the surplus is shared. ZUSAMMENFASSUNG - (Warum Fusionen Profite reduzieren und Aktienpreise steigen lassen) Es wird ein "Mechanismus der Gewinnung eines Vorsprungs durch Fusion" aufgezeigt, der eventuell das empirische Rätsel, warum Fusionen Profite reduzieren und Aktienpreise steigen lassen, erklären kann. Eine Fusion kann starke negative externe Effekte bei den Unternehmen auslösen, die nicht an der Fusion beteiligt sind. Wenn es besser ist ein "Insider" zu sein als ein "Outsider", kann es sein, dass Firmen Fusionieren um dem zuvorzukommen, dass ihre Partner mit jemand anderem fusionieren. Desweiteren ist der Wert eines fusionierenden Unternehmens vor der Fusion niedrig, da er das Risiko ein Outsider zu werden reflektiert. Diese Ergebnisse werden aus einem Modell endogener Fusionen abgeleitet, welches die Bedingungen unter denen eine Fusion stattfindet, wann sie stattfindet und wie der Überschuss verteilt werden wird, vorhersagt.Mergers, Acquisitions, Defensive Mergers, Coalition Formation