Paper:
Adaptive Learning with Unknown Information Flows
An agent facing sequential decisions that are characterized by partial feedback needs to strike a balance between maximizing immediate payoffs based on available information, and acquiring new information that may be essential for maximizing future payoffs. This trade-off is captured by the multi-armed bandit (MAB) framework that has been studied and applied when at each time epoch payoff observations are collected on the actions that are selected at that epoch. In this paper we introduce a new, generalized MAB formulation in which additional information on each arm may appear arbitrarily throughout the decision horizon, and study the impact of such information flows on the achievable performance and the design of efficient decision-making policies. By obtaining matching lower and upper bounds, we characterize the (regret) complexity of this family of MAB problems as a function of the information flows. We introduce an adaptive exploration policy that, without any prior knowledge of the information arrival process, attains the best performance (in terms of regret rate) that is achievable when the information arrival process is a priori known. Our policy uses dynamically customized virtual time indexes to endogenously control the exploration rate based on the realized information arrival process.

Review:
Summary: The paper proposes a new multi-armed bandit (MAB) formulation, in which the agent may observe reward realizations of some of the arms arbitrarily before each round. The paper studies the impact of information flows on regret performance by deriving the regret lower bound with respect to information flows. Moreover, the paper proposes an adaptive exploration policy matching the regret lower bound. However, the insight under this setting is somewhat unclear to the reviewer. Therefore, the reviewer suggests voting for “weak accept”.   Significance: The paper studies the problem of MAB with auxiliary information for some arms. The problem is interesting and has not been studied before. The paper provides an adaptive exploration policy with a near-optimal regret upper bound. However, in each round, it is assumed that the player obtains the knowledge of the arms with auxiliary information before choosing an arm to pull. It is hard to find the motivation for this assumption.   Clarity: This paper is easy to follow. However, the clarity of the motivation can be further improved if the authors can give one or two real-world examples of this MAB formulation, especially for the case where the player observes the impact of information flows before choosing arms to pull. Another minor issue is that this paper does not have a conclusion section to summarize the contributions.   Originality: The originality of this paper comes from the new, generalized MAB problem setting that considers auxiliary information of the arms may arrive arbitrarily between pulls.   Technical Quality: The theoretical analyses are solid and the results are elegant. The algorithms are designed to keep the number of observations of a suboptimal arm be of order log(T), as the number of observations is unequal to the number of pulls. The proofs are regular and correct, with nothing new in the methodology.