Efficient Multinomial Logistic Bandit via Frequent Directions
- URL: http://arxiv.org/abs/2606.11968v1
- Date: Wed, 10 Jun 2026 11:47:27 GMT
- Title: Efficient Multinomial Logistic Bandit via Frequent Directions
- Abstract summary: A representative UCB-type algorithm, OFUL-MLogB, achieves a regret bound of $tildemathcalO(KdsqrtT)$, but still requires $mathcalO(K3d3)$ time and $mathcalO(K2d2)$ space per round.<n>We propose EOFD-MLogB, which integrates frequent directions matrix sketching into OFUL-MLogB.
- Score: 36.600560776380874
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: This paper studies efficient online algorithms for multinomial logistic bandits (MLogB), where the feedback distribution over $K+1$ outcomes follows a multinomial logistic model of $d$-dimensional action vectors. A representative UCB-type algorithm, OFUL-MLogB, achieves a regret bound of $\tilde{\mathcal{O}}(Kd\sqrt{T})$, but still requires $\mathcal{O}(K^3d^3)$ time and $\mathcal{O}(K^2d^2)$ space per round due to parameter estimation and optimistic reward construction, which is prohibitive in high-dimensional settings. To address this limitation, we propose EOFD-MLogB, which integrates frequent directions matrix sketching into OFUL-MLogB. By maintaining a low-rank SVD sketch of the accumulated Hessian, constrained online Newton updates in parameter estimation and $Kd \times K$ spectral-norm computations in the reward bonus are reduced to one-dimensional root-finding tasks and $K \times K$ eigenvalue computations, respectively. This yields dominant per-round time complexity $\mathcal{O}(Kd(m+K)^2)$ and space complexity $\mathcal{O}(Kd(m+K))$, where $m \ll d$ is the sketch size. We further prove a regret bound of $\tilde{\mathcal{O}}(Δ_T(Kd\lnΔ_T+m)\sqrt{T})$, where the sketching error factor $Δ_T$ is controlled by the $m$-truncated spectral tail of the Hessian. Thus, when the Hessian is approximately low-rank, the regret is close to that of OFUL-MLogB. Experiments validate the computational efficiency and competitive performance.
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