Optimal and Efficient Contextual Combinatorial Semi-bandits with General Function Approximation
Provides a computationally efficient and theoretically optimal algorithm for a broad class of combinatorial bandit problems, benefiting applications like slate recommendation and online advertising.
The paper tackles the contextual combinatorial semi-bandit problem with general reward function approximation, proposing SquareCB.Comb, an efficient algorithm that achieves a minimax optimal regret bound of O(√(m A T log|F|)), matching state-of-the-art guarantees in restricted settings while generalizing to arbitrary combinatorial actions.
We study the contextual combinatorial semi-bandit (CCSB) problem with general reward function approximation. At each round, the learner observes a context, selects a combinatorial action consisting of a subset of basic arms, and receives the reward of each selected arm; the goal is to maximize the cumulative reward over time. We propose SquareCB.Comb, a computationally efficient algorithm that, at each round, solves a convex optimization problem to sample a combinatorial action that balances exploration and exploitation. SquareCB.Comb scales to large arm sets and imposes no structural assumptions on the action set beyond a cardinality bound of $m$ on each combinatorial action. We prove that SquareCB.Comb achieves a minimax optimal regret bound of $O(\sqrt{m A T \log |\mathcal{F}|})$, where $A$ is the number of arms, $m$ is the maximum number of arms in a combinatorial action, $T$ is the time horizon, and $\mathcal{F}$ is the reward function class. In the realizable setting, this bound matches the state-of-the-art regret guarantees achieved by policy search-based algorithms in the more restricted slate recommendation settings, while simultaneously generalizing to arbitrary combinatorial action structures and general reward function approximation.