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University of Illinois – Urbana-Champaign

1. Yekkehkhany, Ali. Risk-averse multi-armed bandits and game theory.

Degree: PhD, Electrical & Computer Engr, 2020, University of Illinois – Urbana-Champaign

The multi-armed bandit (MAB) and game theory literature is mainly focused on the expected cumulative reward and the expected payoffs in a game, respectively. In contrast, the rewards and the payoffs are often random variables whose expected values only capture a vague idea of the overall distribution. The focus of this dissertation is to study the fundamental limits of the existing bandits and game theory problems in a risk-averse framework and propose new ideas that address the shortcomings. The author believes that human beings are mostly risk-averse, so studying multi-armed bandits and game theory from the point of view of risk aversion, rather than expected reward/payoff, better captures reality. In this manner, a specific class of multi-armed bandits, called explore-then-commit bandits, and stochastic games are studied in this dissertation, which are based on the notion of Risk-Averse Best Action Decision with Incomplete Information (R-ABADI, Abadi is the maiden name of the author's mother). The goal of the classical multi-armed bandits is to exploit the arm with the maximum score defined as the expected value of the arm reward. Instead, we propose a new definition of score that is derived from the joint distribution of all arm rewards and captures the reward of an arm relative to those of all other arms. We use a similar idea for games and propose a risk-averse R-ABADI equilibrium in game theory that is possibly different from the Nash equilibrium. The payoff distributions are taken into account to derive the risk-averse equilibrium, while the expected payoffs are used to find the Nash equilibrium. The fundamental properties of games, e.g. pure and mixed risk-averse R-ABADI equilibrium and strict dominance, are studied in the new framework and the results are expanded to finite-time games. Furthermore, the stochastic congestion games are studied from a risk-averse perspective and three classes of equilibria are proposed for such games. It is shown by examples that the risk-averse behavior of travelers in a stochastic congestion game can improve the price of anarchy in Pigou and Braess networks. Furthermore, the Braess paradox does not occur to the extent proposed originally when travelers are risk-averse. We also study an online affinity scheduling problem with no prior knowledge of the task arrival rates and processing rates of different task types on different servers. We propose the Blind GB-PANDAS algorithm that utilizes an exploration-exploitation scheme to load balance incoming tasks on servers in an online fashion. We prove that Blind GB-PANDAS is throughput optimal, i.e. it stabilizes the system as long as the task arrival rates are inside the capacity region. The Blind GB-PANDAS algorithm is compared to FCFS, Max-Weight, and c-mu-rule algorithms in terms of average task completion time through simulations, where the same exploration-exploitation approach as Blind GB-PANDAS is used for Max-Weight and c-μ-rule. The extensive simulations show that the Blind GB-PANDAS algorithm conspicuously… Advisors/Committee Members: Nagi, Rakesh (advisor), Nagi, Rakesh (Committee Chair), Hajek, Bruce (committee member), Shomorony, Ilan (committee member), Srikant, Rayadurgam (committee member).

Subjects/Keywords: Online Learning; Multi-Armed Bandits; Exploration-Exploitation; Explore-Then-Commit Bandits; Risk-Aversion; Game Theory; Stochastic Game Theory; Congestion Games; Affinity Scheduling; MapReduce; Data Center

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APA (6th Edition):

Yekkehkhany, A. (2020). Risk-averse multi-armed bandits and game theory. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from

Chicago Manual of Style (16th Edition):

Yekkehkhany, Ali. “Risk-averse multi-armed bandits and game theory.” 2020. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed April 23, 2021.

MLA Handbook (7th Edition):

Yekkehkhany, Ali. “Risk-averse multi-armed bandits and game theory.” 2020. Web. 23 Apr 2021.


Yekkehkhany A. Risk-averse multi-armed bandits and game theory. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2020. [cited 2021 Apr 23]. Available from:

Council of Science Editors:

Yekkehkhany A. Risk-averse multi-armed bandits and game theory. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2020. Available from: