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We consider a linear stochastic bandit problem involving $M$ agents that can collaborate via a central server to minimize regret. A fraction $\alpha$ of these agents are adversarial and can act arbitrarily, leading to the following tension:…

Machine Learning · Computer Science 2022-06-08 Aritra Mitra , Arman Adibi , George J. Pappas , Hamed Hassani

We study the problem of stochastic contextual bandits in the agnostic setting, where the goal is to compete with the best policy in a given class without assuming realizability or imposing model restrictions on losses or rewards. In this…

Machine Learning · Statistics 2026-04-06 Samuel Girard , Aurelien Bibaut , Arthur Gretton , Nathan Kallus , Houssam Zenati

We study the performance guarantees of exploration-free greedy algorithms for the linear contextual bandit problem. We introduce a novel condition, named the \textit{Local Anti-Concentration} (LAC) condition, which enables a greedy bandit…

Machine Learning · Statistics 2025-01-17 Seok-Jin Kim , Min-hwan Oh

A contextual bandit problem is studied in a highly non-stationary environment, which is ubiquitous in various recommender systems due to the time-varying interests of users. Two models with disjoint and hybrid payoffs are considered to…

Machine Learning · Computer Science 2020-03-03 Xiao Xu , Fang Dong , Yanghua Li , Shaojian He , Xin Li

We address the problem of identifying the optimal policy with a fixed confidence level in a multi-armed bandit setup, when \emph{the arms are subject to linear constraints}. Unlike the standard best-arm identification problem which is well…

Machine Learning · Computer Science 2024-01-26 Emil Carlsson , Debabrota Basu , Fredrik D. Johansson , Devdatt Dubhashi

We study contextual bandits with ancillary constraints on resources, which are common in real-world applications such as choosing ads or dynamic pricing of items. We design the first algorithm for solving these problems that handles…

Machine Learning · Computer Science 2015-08-03 Ashwinkumar Badanidiyuru , John Langford , Aleksandrs Slivkins

We study the stochastic contextual bandit problem, where the reward is generated from an unknown function with additive noise. No assumption is made about the reward function other than boundedness. We propose a new algorithm, NeuralUCB,…

Machine Learning · Computer Science 2020-07-03 Dongruo Zhou , Lihong Li , Quanquan Gu

We formulate a new problem at the intersectionof semi-supervised learning and contextual bandits,motivated by several applications including clini-cal trials and ad recommendations. We demonstratehow Graph Convolutional Network (GCN), a…

Machine Learning · Computer Science 2020-10-26 Sohini Upadhyay , Mikhail Yurochkin , Mayank Agarwal , Yasaman Khazaeni , DjallelBouneffouf

We consider contextual linear bandits over networks, a class of sequential decision-making problems where learning occurs simultaneously across multiple locations and the reward distributions share structural similarities while also…

Machine Learning · Computer Science 2025-08-26 Chuyun Deng , Huiwen Jia

Single-player contextual bandits are a well-studied problem in reinforcement learning that has seen applications in various fields such as advertising, healthcare, and finance. In light of the recent work on \emph{information asymmetric}…

Machine Learning · Computer Science 2025-03-13 William Chang , Yuanhao Lu

Contextual bandit algorithms are at the core of many applications, including recommender systems, clinical trials, and optimal portfolio selection. One of the most popular problems studied in the contextual bandit literature is to maximize…

Machine Learning · Computer Science 2023-10-24 Siddhant Chaudhary , Abhishek Sinha

We consider a stochastic contextual bandit problem where the dimension $d$ of the feature vectors is potentially large, however, only a sparse subset of features of cardinality $s_0 \ll d$ affect the reward function. Essentially all…

Machine Learning · Statistics 2021-04-29 Min-hwan Oh , Garud Iyengar , Assaf Zeevi

We consider a novel formulation of the multi-armed bandit model, which we call the contextual bandit with restricted context, where only a limited number of features can be accessed by the learner at every iteration. This novel formulation…

Artificial Intelligence · Computer Science 2017-06-09 Djallel Bouneffouf , Irina Rish , Guillermo A. Cecchi , Raphael Feraud

Contextual bandit algorithms provide principled online learning solutions to balance the exploitation-exploration trade-off in various applications such as recommender systems. However, the learning speed of the traditional contextual…

Machine Learning · Computer Science 2020-01-28 Xiaoying Zhang , Hong Xie , Hang Li , John C. S. Lui

Current endpointing (EP) solutions learn in a supervised framework, which does not allow the model to incorporate feedback and improve in an online setting. Also, it is a common practice to utilize costly grid-search to find the best…

Audio and Speech Processing · Electrical Eng. & Systems 2024-02-09 Do June Min , Andreas Stolcke , Anirudh Raju , Colin Vaz , Di He , Venkatesh Ravichandran , Viet Anh Trinh

Stochastic linear contextual bandit algorithms have substantial applications in practice, such as recommender systems, online advertising, clinical trials, etc. Recent works show that optimal bandit algorithms are vulnerable to adversarial…

Machine Learning · Statistics 2023-01-31 Qin Ding , Cho-Jui Hsieh , James Sharpnack

We investigate the high-dimensional sparse linear bandits problem in a data-poor regime where the time horizon is much smaller than the ambient dimension and number of arms. We study the setting under the additional blocking constraint…

Machine Learning · Computer Science 2025-05-30 Adit Jain , Soumyabrata Pal , Sunav Choudhary , Ramasuri Narayanam , Harshita Chopra , Vikram Krishnamurthy

Despite their success in many domains, large language models (LLMs) remain under-studied in scenarios requiring optimal decision-making under uncertainty. This is crucial as many real-world applications, ranging from personalized…

Machine Learning · Computer Science 2025-07-15 Allen Nie , Yi Su , Bo Chang , Jonathan N. Lee , Ed H. Chi , Quoc V. Le , Minmin Chen

Contextual multi-armed bandit algorithms are widely used in sequential decision tasks such as news article recommendation systems, web page ad placement algorithms, and mobile health. Most of the existing algorithms have regret proportional…

Machine Learning · Statistics 2020-02-14 Gi-Soo Kim , Myunghee Cho Paik

We study a novel variant of the multi-armed bandit problem, where at each time step, the player observes an independently sampled context that determines the arms' mean rewards. However, playing an arm blocks it (across all contexts) for a…

Machine Learning · Computer Science 2020-06-18 Soumya Basu , Orestis Papadigenopoulos , Constantine Caramanis , Sanjay Shakkottai