REVIEW 5 major objections 5 minor 39 references
Multi-Agent Stochastic Bandits Robust to Adversarial Corruptions
T0 review · 5 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read DRAA is a fully distributed, corruption-robust algorithm for heterogeneous multi-agent bandits with regret O((L/Lmin)C + log T * K/Delta_min).
desk verdict First heterogeneous multi-agent corruption-robust bandit paper with a genuinely useful weighted estimator, but the proof of Lemma 2 has a reversed Freedman inequality and false constants, so Theorem 1 is not established as written. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
The authors propose DRAA, a distributed algorithm. Time is split into epochs of growing length. At the start of each epoch, every agent divides its arms into active and bad groups, pulling bad arms only rarely but still often enough to detect if a rating was corrupted. At the end of the epoch, agents broadcast their observations. The key technical step is a weighted estimator: when combining observations from other agents, the algorithm divides each agent's contribution by that agent's probability of pulling the arm, so that agents who rarely pull an arm do not dominate the average. This weighting is what makes the corruption penalty scale with Lmin, the minimum number of agents that share any arm, instead of with the total number of agents.
The main theoretical result is a regret bound. Regret is the reward lost by not always pulling the best local arm. DRAA achieves regret O((L/Lmin)C + log(T) K/Delta_min), where C is the adversary's total corruption budget. In the special cases of one agent, or all agents accessing all arms, this matches known lower bounds, improving on the previous best algorithms by removing a factor of K and of L from the corruption term.
Extended reading notes
Core claim
Theorem 1: with probability at least 1-delta, DRAA (Algorithm 2) achieves regret O((L/Lmin) C + log(KL/delta log T) log T * K/Delta_min) and communication cost O(L log(T log((8K/delta) log T))). If correct, the additive cost of adversarial corruption is linear in the corruption budget C, scaled only by L/Lmin, with no extra factor of K or L in the special cases.
Load-bearing premise
The algorithm requires every agent to know the global arm set K and every other agent's local arm set (Algorithm 2, Input), because epoch lengths are set to T_m = lambda K 2^{2(m-1)}/Lmin and the pull probabilities depend on K and Lk. If agents only know their own arm set, they cannot compute Lmin or synchronize epoch boundaries, and the stated regret bound and communication protocol do not apply. The paper does not discuss relaxing this global-knowledge requirement.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies L-agent K-arm stochastic bandits with adversarial corruption in a heterogeneous setting where each agent has its own local arm set. It proposes DRAA, a fully distributed, epoch-based algorithm in which each agent classifies its local arms as active or bad, assigns pull probabilities based on inverse estimated gaps, broadcasts observed reward sums at epoch boundaries, and forms estimates with a weighted estimator that reweights other agents' observations by inverse pull probabilities. The main result, Theorem 1, claims that with probability at least 1-δ the regret is O((L/Lmin)C + log(KL/δ log T) log T K/Δmin) and the communication cost is O(L log(T log((8K/δ) log T))), where C is the total adversarial corruption budget. The appendix derives the regret through a concentration lemma (Lemma 2), gap-estimate lemmas (Lemmas 3-5), and a three-case regret decomposition, and then specializes the bound to single-agent and homogeneous multi-agent settings, claiming to remove the K and L factors from the corruption term in those cases.
Significance. If the claimed bounds were correct, this would be a valuable first algorithm for heterogeneous multi-agent bandits with adversarial corruption, and the additive O((L/Lmin)C) corruption dependence is an attractive target. The claimed improvements over BARBAR in the single-agent case and over Liu et al. in the homogeneous multi-agent case are also significant, as is the explicit comparison between the weighted and naive estimators. The paper has a clear high-level proof strategy and the algorithm is reasonably described. However, the proof of Lemma 2, which is the cornerstone of every subsequent regret bound, contains several concrete and load-bearing errors: a reversed Freedman tail direction, an invalid |X_t'|≤1 bound, a numerically false lower bound relating the epoch length to the confidence parameter, and a mismatch between the event E that is stated and the event that is actually proved. The significance of the paper is therefore conditional on a corrected analysis.
major comments (5)
- [A.1, Eq. (6) and Eq. (17)] Event E in Eq. (6) is defined with |r^m_{k,ℓ} - μ_k| ≤ 2C^m/(Lmin T^m) + Δ^{m-1}_{k,ℓ}/16, and Lemmas 3-5 and the regret decomposition in Section A.2 all condition on this event. However, the proof of Lemma 2 concludes with Eq. (17), which bounds the same deviation by 2C^m/(Lmin T^m) + Δ^m_{k,ℓ}/16. Since Δ^m_{k,ℓ} and Δ^{m-1}_{k,ℓ} are different random variables, the event actually proved is not the event used later. The proof must be modified to establish E as stated, or the subsequent lemmas must be reworked to use the event that is actually proved.
- [A.1, Eqs. (10)-(15)] The Freedman bound displayed immediately before Eq. (10) is a one-sided upper tail: Pr(Σ_t X_t' ≥ V/b + b ln(4/β)) ≤ β/4. The text then asserts, with probability β/4, a lower bound B^m/(w^m L_k T^m) ≥ 2 w^m Σ|c|/(w^m L_k T^m) + sqrt(...). The upper tail gives the opposite inequality for this direction. A two-sided bound, for instance by applying the same Freedman inequality to {-X_t'}, is required to justify Eq. (15), and it is not written. This is a sign error in the central concentration argument.
- [A.1, paragraph 'Upper bounding |X_t'|'] The bound |X_t'|≤1 is obtained by replacing the factor 2^{-2m-7} in the stated definition w^m_{k,ℓ}=2^{-2m-7} Lmin/(Lk K) (Δ^{m+1}_{k,ℓ})^{-2} with 2^{-2m-13}. With the definition as written, for k∈B^m_{ℓ'} one can only conclude |X_t'| ≤ (Δ^{m+1}_{k,ℓ})^{-2} ≤ 64, because Δ≥2^{-3} by Line 15 of Algorithm 2, not the claimed value 1. The Freedman inequality with b=1 is therefore not applicable as stated. The definition of w^m and the bounding argument must be made consistent.
- [A.1, Eq. (12)] The lower bound w^m_{k,ℓ} L_k T^m ≥ 2^{10} ln(4/β) is numerically false with the announced constants. Substituting T^m=λK2^{2(m-1)}/Lmin and w^m_{k,ℓ}=2^{-2m-7}Lmin/(LkK)(Δ^{m+1}_{k,ℓ})^{-2} gives w^m_{k,ℓ}L_kT^m = λ(Δ^{m+1}_{k,ℓ})^{-2}/512. With λ=224 ln(8KL log T/δ) and β=δ/(2KL log T), this is approximately 0.4375 ln(4/β)(Δ^{m+1}_{k,ℓ})^{-2}, which is at most about 28 ln(4/β). The claimed factor 2^{10} ln(4/β) is off by more than an order of magnitude. Consequently the bound sqrt(4 ln(4/β)/(w^m L_k T^m)) ≤ Δ^m/16 does not follow, and Lemma 2 is not established.
- [A.2, Case 3 and Eqs. (41), (48)] In Case 3 the text states 'if k∈B^{m-1}_ℓ' and then bounds RegB,3 by summing over k∈B^m_ℓ. These are different sets, and the proof does not explain why a bound for B^{m-1}_ℓ can be summed over B^m_ℓ. Given that Case 2 explicitly argued membership in B^m_ℓ, the Case 3 argument needs a matching membership statement for its corruption case. As written this part of the regret decomposition is not rigorous.
minor comments (5)
- [Algorithm 2, Input] The algorithm requires every agent to know the full arm set K and every other agent's local arm set in order to compute Lmin and the epoch lengths. This is a strong global-knowledge assumption for a 'fully distributed' algorithm; it should be stated explicitly and discussed, especially because the epoch boundaries and pull probabilities depend on it.
- [Appendix B, Lemma 6] Lemma 6 is stated with no assertion, and Eq. (33) refers to 'Lemma ??'. The proof of Remark 1 is therefore incomplete as presented.
- [Section 4, paragraph 'Regret Tightness'] The sentence 'the leading term in both cases remains 1/Δ_min' is misleading, since O(K/Δ_min) can be a factor K larger than O(Σ_{k≠k*} 1/Δ_k) when many gaps are near Δ_min. The comparison should be made precise or removed.
- [Throughout] There are frequent typos and OCR-style artifacts, including duplicated words ('if set too high or too low,if set too high or too low'), malformed inequality symbols ('/greaterorequalslant'), and inconsistent subscripts such as Δ^m_{k',ell}. These should be cleaned up before resubmission.
- [Theorem 1] The communication cost is stated without a proof or a precise definition of M, the number of epochs. The authors should specify M = min{m : T^m ≥ T} and prove the O(L log M) communication bound explicitly, since the epoch length depends on λ.
Assumptions & free parameters
free parameters (1)
- lambda (epoch length constant) =
2^24 log(8KL log T / delta)
assumptions (5)
- domain assumption Rewards for each arm are i.i.d. and bounded in [0,1]
- domain assumption The adversary is causal: it sees realized rewards and history, but not the current action, and returns corrupted rewards for all arms before the pull
- domain assumption Agents broadcast in a fully connected network and each knows the global arm set and all local arm sets
- standard math Standard concentration inequalities (Chernoff-Hoeffding and Freedman) hold as stated
- domain assumption Total corruption C is finite, defined as the sum over agents of l-infinity norms of per-round corruption
Cite this review
Pith. "Pith review of Multi-Agent Stochastic Bandits Robust to Adversarial Corruptions." pith.science (2026). https://pith.science/paper/NFTUALSL
@misc{pith2026241108167,
author = {Pith},
title = {Pith review of: Multi-Agent Stochastic Bandits Robust to Adversarial Corruptions},
year = {2026},
howpublished = {\url{https://pith.science/paper/NFTUALSL}},
note = {Machine review of arXiv:2411.08167}
}
abstract
We study the problem of multi-agent multi-armed bandits with adversarial corruption in a heterogeneous setting, where each agent accesses a subset of arms. The adversary can corrupt the reward observations for all agents. Agents share these corrupted rewards with each other, and the objective is to maximize the cumulative total reward of all agents (and not be misled by the adversary). We propose a multi-agent cooperative learning algorithm that is robust to adversarial corruptions. For this newly devised algorithm, we demonstrate that an adversary with an unknown corruption budget $C$ only incurs an additive $O((L / L_{\min}) C)$ term to the standard regret of the model in non-corruption settings, where $L$ is the total number of agents, and $L_{\min}$ is the minimum number of agents with mutual access to an arm. As a side-product, our algorithm also improves the state-of-the-art regret bounds when reducing to both the single-agent and homogeneous multi-agent scenarios, tightening multiplicative $K$ (the number of arms) and $L$ (the number of agents) factors, respectively.
Reference graph
Works this paper leans on
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arXiv 2021
-
[6]
Contextual bandit algorithms with supervised learning guarantees
Alina Beygelzimer, John Langford, Lihong Li, Lev Reyzin, and Robert Schapire. Contextual bandit algorithms with supervised learning guarantees. In Proceedings of the Fourteenth International Conference on Artificial Intelligence and Statistics, pp.\ 19--26. JMLR Workshop and Conference Proceedings, 2011
work page 2011
-
[7]
Stochastic linear bandits robust to adversarial attacks
Ilija Bogunovic, Arpan Losalka, Andreas Krause, and Jonathan Scarlett. Stochastic linear bandits robust to adversarial attacks. In International Conference on Artificial Intelligence and Statistics, pp.\ 991--999. PMLR, 2021
work page 2021
-
[8]
Collaborative Multi-Agent Heterogeneous Multi-Armed Bandits
Ronshee Chawla, Daniel Vial, Sanjay Shakkottai, and R Srikant. Collaborative multi-agent heterogeneous multi-armed bandits. arXiv preprint arXiv:2305.18784, 2023
work page Pith review arXiv 2023
Show all 39 references
-
[9]
Contextual bandits with linear payoff functions
Wei Chu, Lihong Li, Lev Reyzin, and Robert Schapire. Contextual bandits with linear payoff functions. In Proceedings of the Fourteenth International Conference on Artificial Intelligence and Statistics, pp.\ 208--214. JMLR Workshop and Conference Proceedings, 2011
2011
-
[10]
Concentration of measure for the analysis of randomized algorithms
Devdatt P Dubhashi and Alessandro Panconesi. Concentration of measure for the analysis of randomized algorithms. Cambridge University Press, 2009
2009
-
[11]
Action elimination and stopping conditions for the multi-armed bandit and reinforcement learning problems
Eyal Even-Dar, Shie Mannor, Yishay Mansour, and Sridhar Mahadevan. Action elimination and stopping conditions for the multi-armed bandit and reinforcement learning problems. Journal of machine learning research, 7 0 (6), 2006
2006
-
[12]
Better algorithms for stochastic bandits with adversarial corruptions
Anupam Gupta, Tomer Koren, and Kunal Talwar. Better algorithms for stochastic bandits with adversarial corruptions. In Conference on Learning Theory, pp.\ 1562--1578. PMLR, 2019
2019
-
[13]
Distributed exploration in multi-armed bandits
Eshcar Hillel, Zohar S Karnin, Tomer Koren, Ronny Lempel, and Oren Somekh. Distributed exploration in multi-armed bandits. Advances in Neural Information Processing Systems, 26, 2013
2013
-
[14]
Bayesian exploration with heterogeneous agents
Nicole Immorlica, Jieming Mao, Aleksandrs Slivkins, and Zhiwei Steven Wu. Bayesian exploration with heterogeneous agents. In The world wide web conference, pp.\ 751--761, 2019
2019
-
[15]
Corruption-tolerant bandit learning
Sayash Kapoor, Kumar Kshitij Patel, and Purushottam Kar. Corruption-tolerant bandit learning. Machine Learning, 108 0 (4): 0 687--715, 2019
2019
-
[16]
Cooperative stochastic multi-agent multi-armed bandits robust to adversarial corruptions
Junyan Liu, Shuai Li, and Dapeng Li. Cooperative stochastic multi-agent multi-armed bandits robust to adversarial corruptions. arXiv preprint arXiv:2106.04207, 2021
2021 arXiv
-
[17]
Distributed learning in multi-armed bandit with multiple players
Keqin Liu and Qing Zhao. Distributed learning in multi-armed bandit with multiple players. IEEE transactions on signal processing, 58 0 (11): 0 5667--5681, 2010
2010
-
[18]
Stochastic bandits robust to adversarial corruptions
Thodoris Lykouris, Vahab Mirrokni, and Renato Paes Leme. Stochastic bandits robust to adversarial corruptions. In Proceedings of the 50th Annual ACM SIGACT Symposium on Theory of Computing, pp.\ 114--122, 2018
2018
-
[19]
Multi-player bandits robust to adversarial collisions
Shivakumar Mahesh, Anshuka Rangi, Haifeng Xu, and Long Tran-Thanh. Multi-player bandits robust to adversarial collisions. arXiv preprint arXiv:2211.07817, 2022
2022 arXiv
-
[20]
A practical algorithm for multiplayer bandits when arm means vary among players
Abbas Mehrabian, Etienne Boursier, Emilie Kaufmann, and Vianney Perchet. A practical algorithm for multiplayer bandits when arm means vary among players. In International Conference on Artificial Intelligence and Statistics, pp.\ 1211--1221. PMLR, 2020
2020
-
[21]
Robust federated best-arm identification in multi-armed bandits
Aritra Mitra, Hamed Hassani, and George Pappas. Robust federated best-arm identification in multi-armed bandits. arXiv e-prints, pp.\ arXiv--2109, 2021
2021
-
[22]
Heterogeneous multi-player multi-armed bandits: Closing the gap and generalization
Chengshuai Shi, Wei Xiong, Cong Shen, and Jing Yang. Heterogeneous multi-player multi-armed bandits: Closing the gap and generalization. Advances in neural information processing systems, 34: 0 22392--22404, 2021
2021
-
[23]
Multi-armed bandits in recommendation systems: A survey of the state-of-the-art and future directions
N \' collas Silva, Heitor Werneck, Thiago Silva, Adriano CM Pereira, and Leonardo Rocha. Multi-armed bandits in recommendation systems: A survey of the state-of-the-art and future directions. Expert Systems with Applications, 197: 0 116669, 2022
2022
-
[24]
Stochastic online shortest path routing: The value of feedback
Mohammad Sadegh Talebi, Zhenhua Zou, Richard Combes, Alexandre Proutiere, and Mikael Johansson. Stochastic online shortest path routing: The value of feedback. IEEE Transactions on Automatic Control, 63 0 (4): 0 915--930, 2017
2017
-
[25]
Robust multi-agent multi-armed bandits
Daniel Vial, Sanjay Shakkottai, and R Srikant. Robust multi-agent multi-armed bandits. In Proceedings of the Twenty-second International Symposium on Theory, Algorithmic Foundations, and Protocol Design for Mobile Networks and Mobile Computing, pp.\ 161--170, 2021
2021
-
[26]
Robust multi-agent bandits over undirected graphs
Daniel Vial, Sanjay Shakkottai, and R Srikant. Robust multi-agent bandits over undirected graphs. Proceedings of the ACM on Measurement and Analysis of Computing Systems, 6 0 (3): 0 1--57, 2022
2022
-
[27]
Optimal algorithms for multiplayer multi-armed bandits
Po-An Wang, Alexandre Proutiere, Kaito Ariu, Yassir Jedra, and Alessio Russo. Optimal algorithms for multiplayer multi-armed bandits. In International Conference on Artificial Intelligence and Statistics, pp.\ 4120--4129. PMLR, 2020
2020
-
[28]
Achieving near-optimal individual regret & low communications in multi-agent bandits
Xuchuang Wang, Lin Yang, Yu-Zhen Janice Chen, Xutong Liu, Mohammad Hajiesmaili, Don Towsley, and John CS Lui. Achieving near-optimal individual regret & low communications in multi-agent bandits. In The Eleventh International Conference on Learning Representations, 2023 a
2023
-
[29]
Xuchuang Wang, Lin Yang, Yu-zhen Janice Chen, Xutong Liu, Mohammad Hajiesmaili, Don Towsley, and John C.S. Lui. Achieve near-optimal individual regret & low communications in multi-agent bandits. In International Conference on Learning Representations, 2023 b
2023
-
[30]
Xuchuang Wang, Lin Yang, Yu-zhen Janice Chen, Xutong Liu, Mohammad Hajiesmaili, Don Towsley, and John C.S. Lui. Exploration for free: How does reward heterogeneity improve regret in cooperative multi-agent bandits? In The 39th Conference on Uncertainty in Artificial Intelligen...
2023
-
[31]
A model selection approach for corruption robust reinforcement learning
Chen-Yu Wei, Christoph Dann, and Julian Zimmert. A model selection approach for corruption robust reinforcement learning. In International Conference on Algorithmic Learning Theory, pp.\ 1043--1096. PMLR, 2022
2022
-
[32]
Adversarial bandits with corruptions: Regret lower bound and no-regret algorithm
Lin Yang, Mohammad Hajiesmaili, Mohammad Sadegh Talebi, John Lui, Wing Shing Wong, et al. Adversarial bandits with corruptions: Regret lower bound and no-regret algorithm. Advances in Neural Information Processing Systems, 33: 0 19943--19952, 2020
2020
-
[33]
Cooperative stochastic bandits with asynchronous agents and constrained feedback
Lin Yang, Yu-Zhen Janice Chen, Stephen Pasteris, Mohammad Hajiesmaili, John Lui, and Don Towsley. Cooperative stochastic bandits with asynchronous agents and constrained feedback. Advances in Neural Information Processing Systems, 34: 0 8885--8897, 2021
2021
-
[34]
Distributed bandits with heterogeneous agents
Lin Yang, Yu-Zhen Janice Chen, Mohammad H Hajiemaili, John CS Lui, and Don Towsley. Distributed bandits with heterogeneous agents. In IEEE INFOCOM 2022-IEEE Conference on Computer Communications, pp.\ 200--209. IEEE, 2022
2022
-
[35]
Linear contextual bandits with adversarial corruptions
Heyang Zhao, Dongruo Zhou, and Quanquan Gu. Linear contextual bandits with adversarial corruptions. arXiv preprint arXiv:2110.12615, 2021
2021 arXiv
-
[36]
A privacy-preserving distributed contextual federated online learning framework with big data support in social recommender systems
Pan Zhou, Kehao Wang, Linke Guo, Shimin Gong, and Bolong Zheng. A privacy-preserving distributed contextual federated online learning framework with big data support in social recommender systems. IEEE Transactions on Knowledge and Data Engineering, 33 0 (3): 0 824--838, 2019 a
2019
-
[37]
Toward optimal adaptive online shortest path routing with acceleration under jamming attack
Pan Zhou, Jie Xu, Wei Wang, Yuchong Hu, Dapeng Oliver Wu, and Shouling Ji. Toward optimal adaptive online shortest path routing with acceleration under jamming attack. IEEE/ACM transactions on networking, 27 0 (5): 0 1815--1829, 2019 b
2019
-
[38]
Tsallis-inf: An optimal algorithm for stochastic and adversarial bandits
Julian Zimmert and Yevgeny Seldin. Tsallis-inf: An optimal algorithm for stochastic and adversarial bandits. The Journal of Machine Learning Research, 22 0 (1): 0 1310--1358, 2021
2021
-
[39]
Online shortest path routing: The value of information
Zhenhua Zou, Alexandre Proutiere, and Mikael Johansson. Online shortest path routing: The value of information. In 2014 American Control Conference, pp.\ 2142--2147. IEEE, 2014
2014
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