Economics

Permanent URI for this collectionhttps://hdl.handle.net/10679/316

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Browsing by Author "Caskurlu, B."

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    On efficient computation of equilibrium under social coalition structures
    (TÜBİTAK) Caskurlu, B.; Ekici, Özgür; Kizilkaya, F. E.; Economics; EKİCİ, Özgün
    In game-theoretic settings the key notion of analysis is an equilibrium, which is a profile of agent strategies such that no viable coalition of agents can improve upon their coalitional welfare by jointly changing their strategies. A Nash equilibrium, where viable coalitions are only singletons, and a super strong equilibrium, where every coalition is deemed viable, are two extreme scenarios in regard to coalition formation. A recent trend in the literature is to consider equilibrium notions that allow for coalition formation in between these two extremes and which are suitable to model social coalition structures that arise in various real-life settings. The recent literature considered the question on the existence of equilibria under social coalition structures mainly in Resource Selection Games (RSGs), due to the simplicity of this game form and its wide range of application domains. We take the question on the existence of equilibria under social coalition structures from the perspective of computational complexity theory. We study the problem of deciding the existence of an equilibrium in RSGs with respect to a given social coalition structure. For an arbitrary coalition structure, we show that it is computationally intractable to decide whether an equilibrium exists even in very restricted settings of RSGs. In certain settings where an equilibrium is guaranteed to exist we give polynomial-time algorithms to find an equilibrium.
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    On existence of equilibrium under social coalition structures
    (Springer, 2020) Caskurlu, B.; Ekici, Özgün; Kizilkaya, F. E.; Economics; Chen, J.; Feng, Q.; Xu, J.; EKİCİ, Özgün
    In a strategic form game, a strategy profile is an equilibrium if no viable coalition of agents benefits (in the Pareto sense) from jointly changing their strategies. Weaker or stronger equilibrium notions can be defined by considering various restrictions on coalition formation. In a Nash equilibrium, for instance, the assumption is that viable coalitions are singletons, and in a super strong equilibrium, every coalition is viable. Restrictions on coalition formation can be justified by communication, coordination or institutional constraints. In this paper, inspired by social structures in various real-life scenarios, we introduce certain restrictions on coalition formation, and on their basis, we introduce a number of equilibrium notions. We study our equilibrium notions in resource selection games (RSGs), and we present a complete set of existence and non-existence results for general RSGs and their important special cases.
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    On existence of equilibrium under social coalition structures
    (Cambridge University Press, 2022-02) Caskurlu, B.; Ekici, Özgün; Kizilkaya, F. E.; Economics; EKİCİ, Özgün
    In a strategic-form game, a strategy profile is an equilibrium if no viable coalition of agents (or players) benefits (in the Pareto sense) from jointly changing their strategies. Weaker or stronger equilibrium notions can be defined by considering various restrictions on coalition formation. For instance, in a Nash equilibrium, it is assumed that viable coalitions are singletons, and in a super strong equilibrium, it is assumed that every coalition is viable. Restrictions on coalition formation can be justified by communication limitations, coordination problems, or institutional constraints. In this paper, inspired by social structures in various real-life scenarios, we introduce certain restrictions on coalition formation, and on their basis, we introduce a number of equilibrium notions. As an application, we study our equilibrium notions in resource selection games (RSGs), and we present a complete set of existence and nonexistence results for general RSGs and their important special cases.
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    On singleton congestion games with resilience against collusion
    (Springer, 2021) Caskurlu, B.; Ekici, Özgün; Kızılkaya, F. E.; Economics; EKİCİ, Özgün
    We study the subclass of singleton congestion games in which there are identical resources with increasing cost functions. In this domain, we prove that there always exists an outcome that is resilient to weakly-improving deviations by singletons (i.e., the outcome is a Nash equilibrium), by the grand coalition (i.e., the outcome is Pareto efficient), and by coalitions with respect to an a priori given partition coalition structure (i.e., the outcome is a partition equilibrium). To our knowledge, this is the strongest existence guarantee in the literature on congestion games when weakly-improving deviations are considered. Our proof technique gives the false impression of a potential function argument but it is a novel application of proof by contradiction.