Best Arm Identification for Cascading Bandits in the Fixed Confidence Setting

Abstract

We design and analyze CASCADEBAI, an algorithm for finding the best set of K items, also called an arm, within the framework of cascading bandits. An upper bound on the time complexity of CASCADEBAI is derived by overcoming a crucial analytical challenge, namely, that of probabilistically estimating the amount of available feedback at each step. To do so, we define a new class of random variables (r.v.’s) which we term asleft-sidedsub-Gaussianr.v.’s;theseclassisarelaxed version of sub-Gaussian r.v.’s. This enables the application of a sufficiently tight Bernsteintype concentration inequality. We show, through the derivation of a lower bound on the time complexity, that the performance of CASCADEBAI is optimal in some practical regimes. Finally, extensive numerical simulations corroborate the efficacy of CASCADEBAI as well as the tightness of our upper bound on its time complexity.