Fair Algorithms for Multi-Agent Multi-Armed Bandits

Safwan Hossain, Evi Micha, Nisarg Shah

Keywords: fairness, multi-armed bandits, Nash welfare

TL;DR: We propose a multi-agent multi-armed bandit problem, in which pulling an arm generates a different stochastic reward for each agent, and design algorithms with sublinear regret in the Nash welfare fairness measure.

Abstract: We propose a multi-agent variant of the classical multi-armed bandit problem, in which there are $N$ agents and $K$ arms, and pulling an arm generates a (possibly different) stochastic reward for each agent. Unlike the classical multi-armed bandit problem, the goal is not to learn the "best arm"; indeed, each agent may perceive a different arm to be the best for her personally. Instead, we seek to learn a fair distribution over the arms. Drawing on a long line of research in economics and computer science, we use the Nash social welfare as our notion of fairness. We design multi-agent variants of three classic multi-armed bandit algorithms and show that they achieve sublinear regret, which is now measured in terms of the lost Nash social welfare. We also extend a classical lower bound, establishing the optimality of one of our algorithms.

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