We revisit the study of optimal regret rates in bandit combinatorial optimization---a fundamental framework for sequential decision making under uncertainty that abstracts numerous combinatorial prediction problems. We prove that the attainable regret in this setting grows as $\widetildeΘ(k^{3/2}\sqrt{dT})$ where $d$ is the dimension of the problem and $k$ is a bound over the maximal instantaneous loss, disproving a conjecture of Audibert, Bubeck, and Lugosi (2013) who argued that the optimal rate should be of the form $\widetildeΘ(k\sqrt{dT})$. Our bounds apply to several important instances of the framework, and in particular, imply a tight bound for the well-studied bandit shortest path problem. By that, we also resolve an open problem posed by Cesa-Bianchi and Lugosi (2012).
Chalmers University of Technology（查尔姆斯理工大学）；Volvo Car Corporation（沃尔沃汽车公司）
Bottleneck identification is a challenging task in network analysis, especially when the network is not fully specified. To address this task, we develop a unified online learning framework based on combinatorial semi-bandits that performs bottleneck identification in parallel with learning the specifications of the underlying network. Within this framework, we adapt and study various combinatorial semi-bandit methods such as epsilon-greedy, LinUCB, BayesUCB, NeuralUCB, and Thompson Sampling. In addition, our framework is capable of using contextual information in the form of contextual bandit…
In this paper, we study an interesting combination of sleeping and combinatorial stochastic bandits. In the mixed model studied here, at each discrete time instant, an arbitrary \emph{availability set} is generated from a fixed set of \emph{base} arms. An algorithm can select a subset of arms from the \emph{availability set} (sleeping bandits) and receive the corresponding reward along with semi-bandit feedback (combinatorial bandits). We adapt the well-known CUCB algorithm in the sleeping combinatorial bandits setting and refer to it as \CSUCB. We prove -- under mild smoothness conditions -- …
Peking University（北京大学）；University of Minnesota（明尼苏达大学）；Microsoft Research（微软研究院）；Carnegie Mellon University（卡内基梅隆大学）
Consider a bandit algorithm that recommends actions to self-interested users in a recommendation system. The users are free to choose other actions and need to be incentivized to follow the algorithm's recommendations. While the users prefer to exploit, the algorithm can incentivize them to explore by leveraging the information collected from the previous users. All published work on this problem, known as incentivized exploration, focuses on small, unstructured action sets and mainly targets the case when the users' beliefs are independent across actions. However, realistic exploration proble…
Tsinghua University（清华大学）；Institute for Interdisciplinary Information Sciences（交叉信息研究院）
We consider the stochastic combinatorial semi-bandit problem with adversarial corruptions. We provide a simple combinatorial algorithm that can achieve a regret of $\tilde{O}\left(C+d^2K/Δ_{min}\right)$ where $C$ is the total amount of corruptions, $d$ is the maximal number of arms one can play in each round, $K$ is the number of arms. If one selects only one arm in each round, we achieves a regret of $\tilde{O}\left(C+\sum_{Δ_i>0}(1/Δ_i)\right)$. Our algorithm is combinatorial and improves on the previous combinatorial algorithm by [Gupta et al., COLT2019] (their bound is $\tilde{O}\left(KC+\…
We consider combinatorial semi-bandits with uncorrelated Gaussian rewards. In this article, we propose the first method, to the best of our knowledge, that enables to compute the solution of the Graves-Lai optimization problem in polynomial time for many combinatorial structures of interest. In turn, this immediately yields the first known approach to implement asymptotically optimal algorithms in polynomial time for combinatorial semi-bandits.
Top-k Combinatorial Bandits with Full-Bandit Feedback
Tel Aviv University（特拉维夫大学）；Google Research（谷歌研究院）
Top-k组合强盗一般化多武器强盗，其中在每一轮可以选择$n$武器中的任何$k$子集，并且获得奖励的总和。我们解决全强盗反馈，其中代理人只观察奖励的总和，与半强盗反馈，其中代理人也观察个别武器的奖励。我们提出了组合连续接受和拒绝（CSAR）算法，它将SAR（Bubeck et al，2013）推广到top-k组合强盗。我们的主要贡献是一个有效的抽样计划，使用阿达玛矩阵，以准确地估计个人武器的预期回报。我们讨论了两个变种的算法，第一个最大限度地减少样本的复杂性，第二个最小化的遗憾。我们还证明了一个下界的样本复杂性，这是紧的$k=O(1)$。最后，我们进行了实验，并表明我们的算法优于其他方法。
In this paper, we study the stochastic combinatorial multi-armed bandit problem under semi-bandit feedback. While much work has been done on algorithms that optimize the expected reward for linear as well as some general reward functions, we study a variant of the problem, where the objective is to be risk-aware. More specifically, we consider the problem of maximizing the Conditional Value-at-Risk (CVaR), a risk measure that takes into account only the worst-case rewards. We propose new algorithms that maximize the CVaR of the rewards obtained from the super arms of the combinatorial bandit f…
A Near-Optimal Change-Detection Based Algorithm for Piecewise-Stationary Combinatorial Semi-Bandits
UIUC（伊利诺伊大学厄巴纳-香槟分校）；SMU（新加坡管理大学）
研究了分段平稳组合半强盗问题。与原来的组合半强盗问题相比，我们的设置假设的奖励分布的基础武器可能会改变在一个分段固定的方式在未知的时间步长。我们提出了一种算法，\texttt{GLR-CUCB}，它采用了一种有效的组合半强盗算法，\texttt{CUCB}，几乎无参数的变点检测器，\emph{Generalized Likelihood Ratio Test}（GLRT）。我们的分析表明，\texttt{GLR-CUCB}的遗憾是上界由$\mathcal{O}(\sqrt{NKT\log{T}})$，其中$N$是分段固定段的数量，$K$是基本臂的数量，和$T$是时间步的数量。作为补充，我们还得到了一个几乎匹配的遗憾下界的顺序$Ω(\sqrt{NKT}$），分段固定的多臂土匪和组合半土匪，使用信息理论技术和明智地构建分段固定的土匪实例。我们的下限比最好的遗憾下限$Ω(\sqrt{T})$更紧。在合成数据集和真实数据集上的数值实验证明了\texttt{GLR-CUCB}算法相对于其他最先进算法的优越性。
Conservative mechanism is a desirable property in decision-making problems which balance the tradeoff between the exploration and exploitation. We propose the novel \emph{conservative contextual combinatorial cascading bandit ($C^4$-bandit)}, a cascading online learning game which incorporates the conservative mechanism. At each time step, the learning agent is given some contexts and has to recommend a list of items but not worse than the base strategy and then observes the reward by some stopping rules. We design the $C^4$-UCB algorithm to solve the problem and prove its n-step upper regret …
New York University（纽约大学）；Stanford University（斯坦福大学）；University of Florida（佛罗里达大学）
In this paper we study the adversarial combinatorial bandit with a known non-linear reward function, extending existing work on adversarial linear combinatorial bandit. {The adversarial combinatorial bandit with general non-linear reward is an important open problem in bandit literature, and it is still unclear whether there is a significant gap from the case of linear reward, stochastic bandit, or semi-bandit feedback.} We show that, with $N$ arms and subsets of $K$ arms being chosen at each of $T$ time periods, the minimax optimal regret is $\widetildeΘ_{d}(\sqrt{N^d T})$ if the reward funct…
Inria Lille（里尔法国国家信息与自动化研究所）；ENS Paris-Saclay（巴黎萨克雷高等师范学院）；ENSAE（法国国家统计与经济管理学院）；Criteo AI Lab（Criteo人工智能实验室）；DeepMind Paris（巴黎DeepMind）
We investigate stochastic combinatorial multi-armed bandit with semi-bandit feedback (CMAB). In CMAB, the question of the existence of an efficient policy with an optimal asymptotic regret (up to a factor poly-logarithmic with the action size) is still open for many families of distributions, including mutually independent outcomes, and more generally the multivariate sub-Gaussian family. We propose to answer the above question for these two families by analyzing variants of the Combinatorial Thompson Sampling policy (CTS). For mutually independent outcomes in $[0,1]$, we propose a tight analy…
University of Tübingen（图宾根大学）；Technical University of Berlin（柏林工业大学）
In a sequential decision-making problem, having a structural dependency amongst the reward distributions associated with the arms makes it challenging to identify a subset of alternatives that guarantees the optimal collective outcome. Thus, besides individual actions' reward, learning the causal relations is essential to improve the decision-making strategy. To solve the two-fold learning problem described above, we develop the 'combinatorial semi-bandit framework with causally related rewards', where we model the causal relations by a directed graph in a stationary structural equation model.…
Technion – Institute of Technology（以色列理工学院）；Meta；Nvidia Research（英伟达研究院）
We consider a stochastic multi-armed bandit setting where reward must be actively queried for it to be observed. We provide tight lower and upper problem-dependent guarantees on both the regret and the number of queries. Interestingly, we prove that there is a fundamental difference between problems with a unique and multiple optimal arms, unlike in the standard multi-armed bandit problem. We also present a new, simple, UCB-style sampling concept, and show that it naturally adapts to the number of optimal arms and achieves tight regret and querying bounds.
Paderborn University（帕德博恩大学）；University of Munich (LMU)（慕尼黑大学）；Munich Center for Machine Learning（慕尼黑机器学习中心）
We consider the combinatorial bandits problem with semi-bandit feedback under finite sampling budget constraints, in which the learner can carry out its action only for a limited number of times specified by an overall budget. The action is to choose a set of arms, whereupon feedback for each arm in the chosen set is received. Unlike existing works, we study this problem in a non-stochastic setting with subset-dependent feedback, i.e., the semi-bandit feedback received could be generated by an oblivious adversary and also might depend on the chosen set of arms. In addition, we consider a gener…
The Chinese University of Hong Kong（香港中文大学）；Shanghai Jiao Tong University（上海交通大学）；Tencent（腾讯）
The problem of multi-armed bandits (MAB) asks to make sequential decisions while balancing between exploitation and exploration, and have been successfully applied to a wide range of practical scenarios. Various algorithms have been designed to achieve a high reward in a long term. However, its short-term performance might be rather low, which is injurious in risk sensitive applications. Building on previous work of conservative bandits, we bring up a framework of contextual combinatorial conservative bandits. An algorithm is presented and a regret bound of $\tilde O(d^2+d\sqrt{T})$ is proven,…
Combinatorial bandits with semi-bandit feedback generalize multi-armed bandits, where the agent chooses sets of arms and observes a noisy reward for each arm contained in the chosen set. The action set satisfies a given structure such as forming a base of a matroid or a path in a graph. We focus on the pure-exploration problem of identifying the best arm with fixed confidence, as well as a more general setting, where the structure of the answer set differs from the one of the action set. Using the recently popularized game framework, we interpret this problem as a sequential zero-sum game and …
Tsinghua University（清华大学）；Microsoft Research Asia（微软亚洲研究院）
In this paper, we study the application of the Thompson sampling (TS) methodology to the stochastic combinatorial multi-armed bandit (CMAB) framework. We first analyze the standard TS algorithm for the general CMAB model when the outcome distributions of all the base arms are independent, and obtain a distribution-dependent regret bound of $O(m\log K_{\max}\log T / Δ_{\min})$, where $m$ is the number of base arms, $K_{\max}$ is the size of the largest super arm, $T$ is the time horizon, and $Δ_{\min}$ is the minimum gap between the expected reward of the optimal solution and any non-optimal so…
Efficient Swap Regret Minimization in Combinatorial Bandits
National Technical University of Athens（雅典国立技术大学）；National and Kapodistrian University of Athens（雅典国立卡波季斯特里安大学）；Archimedes, Athena Research Center（雅典娜研究中心阿基米德部）；Univ. Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；CNRS（法国国家科学研究中心）；Inria（法国国家信息与自动化研究所）；Grenoble INP（格勒诺布尔国立高等物理、数学与信息学院）；University of California, Irvine（加州大学尔湾分校）
The University of Texas at Austin（得克萨斯大学奥斯汀分校）；Amazon（亚马逊）
We consider the combinatorial bandits problem, where at each time step, the online learner selects a size-$k$ subset $s$ from the arms set $\mathcal{A}$, where $\left|\mathcal{A}\right| = n$, and observes a stochastic reward of each arm in the selected set $s$. The goal of the online learner is to minimize the regret, induced by not selecting $s^*$ which maximizes the expected total reward. Specifically, we focus on a challenging setting where 1) the reward distribution of an arm depends on the set $s$ it is part of, and crucially 2) there is \textit{no total order} for the arms in $\mathcal{A…
Volvo Car Corporation（沃尔沃汽车公司）；Chalmers University of Technology（查尔姆斯理工大学）
In this work, we address the problem of long-distance navigation for battery electric vehicles (BEVs), where one or more charging sessions are required to reach the intended destination. We consider the availability and performance of the charging stations to be unknown and stochastic, and develop a combinatorial semi-bandit framework for exploring the road network to learn the parameters of the queue time and charging power distributions. Within this framework, we first outline a pre-processing for the road network graph to handle the constrained combinatorial optimization problem in an effic…
We study the sequential resource allocation problem where a decision maker repeatedly allocates budgets between resources. Motivating examples include allocating limited computing time or wireless spectrum bands to multiple users (i.e., resources). At each timestep, the decision maker should distribute its available budgets among different resources to maximize the expected reward, or equivalently to minimize the cumulative regret. In doing so, the decision maker should learn the value of the resources allocated for each user from feedback on each user's received reward. For example, users may…
Combinatorial Multivariant Multi-Armed Bandits with Applications to Episodic Reinforcement Learning and Beyond
The Chinese University of Hong Kong（香港中文大学）；University of Massachusetts Amherst（马萨诸塞大学阿默斯特分校）；Microsoft Research（微软研究院）；Shanghai Jiao Tong University（上海交通大学）
Optimal Arm Elimination Algorithms for Combinatorial Bandits
Courant Institute of Mathematical Sciences, New York University（Courant数学科学研究所，纽约大学）；Center for Data Science, New York University（数据科学中心，纽约大学）；Stern School of Business, New York University（商学院，纽约大学）；Arena Technologies（Arena技术公司）
The Chinese University of Hong Kong, Shenzhen（香港中文大学（深圳））；Shanghai Jiao Tong University（上海交通大学）
Strategic behavior against sequential learning methods, such as "click framing" in real recommendation systems, have been widely observed. Motivated by such behavior we study the problem of combinatorial multi-armed bandits (CMAB) under strategic manipulations of rewards, where each arm can modify the emitted reward signals for its own interest. This characterization of the adversarial behavior is a relaxation of previously well-studied settings such as adversarial attacks and adversarial corruption. We propose a strategic variant of the combinatorial UCB algorithm, which has a regret of at mo…
Preventing poaching through ranger patrols protects endangered wildlife, directly contributing to the UN Sustainable Development Goal 15 of life on land. Combinatorial bandits have been used to allocate limited patrol resources, but existing approaches overlook the fact that each location is home to multiple species in varying proportions, so a patrol benefits each species to differing degrees. When some species are more vulnerable, we ought to offer more protection to these animals; unfortunately, existing combinatorial bandit approaches do not offer a way to prioritize important species. To …
An efficient algorithm for learning with semi-bandit feedback
Budapest University of Technology and Economics（布达佩斯技术与经济大学）；MTA SZTAKI Institute for Computer Science and Control（MTA SZTAKI计算机科学与控制研究所）；ETH Zürich（苏黎世联邦理工学院）
Thompson Sampling for Combinatorial Semi-bandits with Sleeping Arms and Long-Term Fairness Constraints
University of Victoria（维多利亚大学）；Southeast University（东南大学）；Harbin Institute of Technology（哈尔滨工业大学）
研究了具有长期公平性约束的组合睡眠多臂半强盗问题~（CSMAB-F）。针对该问题，采用Thompson Sampling~（TS）方法最大化总报酬，采用虚拟队列技术处理公平性约束，并设计了一种算法\emph{TS with beta priors and Bernoulli likelihoods for CSMAB-F~(TSCSF-B)}。进一步，我们证明了TSCSF-B能满足公平性约束，并且时间平均后悔的上界为$\frac{N}{2η} + O\left(\frac{\sqrt{mNT\ln T}}{T}\right)$，其中$N$是总的手臂数，$m$是每轮中能同时拉动的最大手臂数~（基数约束），$η$是公平性与奖励的权衡参数.通过放松公平性约束（即，令$η\rightarrow \infty$），该界归结为组合睡眠多臂半强盗问题TS算法的第一个与问题无关的界。最后，我们进行了数值实验，并使用一个高收视率的电影推荐应用程序，以显示所提出的算法的有效性和效率。
