# Exploration by Optimization with Hybrid Regularizers: Logarithmic Regret with Adversarial Robustness in Partial Monitoring

arXiv: https://arxiv.org/abs/2402.08321 · HTML: https://mlsanity.com/paper/2402.08321/

## Key facts

- Cited by 3 papers in the map (data through 14 Oct 2026).
- Builds on 21 of its 38 references that are in the map.
- First posted on arXiv 13 Feb 2024.

## Builds on (most cited first, 21 of 21)

- [Convex optimization](https://mlsanity.com/paper/2106.01946/) (2021)
- [Online Learning: A Modern Introduction Using Convex Optimization](https://mlsanity.com/paper/1912.13213/) (2019)
- [Tsallis-INF: An Optimal Algorithm for Stochastic and Adversarial Bandits](https://mlsanity.com/paper/1807.07623/) (2018)
- [Stochastic bandits robust to adversarial corruptions](https://mlsanity.com/paper/1803.09353/) (2018)
- [More Adaptive Algorithms for Adversarial Bandits](https://mlsanity.com/paper/1801.03265/) (2018)
- [A Second-order Bound with Excess Losses](https://mlsanity.com/paper/1402.2044/) (2014)
- [Beating Stochastic and Adversarial Semi-bandits Optimally and Simultaneously](https://mlsanity.com/paper/1901.08779/) (2019)
- [An Information-Theoretic Approach to Minimax Regret in Partial Monitoring](https://mlsanity.com/paper/1902.00470/) (2019)
- [Mirror Descent and the Information Ratio](https://mlsanity.com/paper/2009.12228/) (2020)
- [On the Complexity of Adversarial Decision Making](https://mlsanity.com/paper/2206.13063/) (2022)
- [A Blackbox Approach to Best of Both Worlds in Bandits and Beyond](https://mlsanity.com/paper/2302.09739/) (2023)
- [Nearly Optimal Best-of-Both-Worlds Algorithms for Online Learning with Feedback Graphs](https://mlsanity.com/paper/2206.00873/) (2022)
- [Exploration by Optimisation in Partial Monitoring](https://mlsanity.com/paper/1907.05772/) (2019)
- [Best-of-Both-Worlds Algorithms for Partial Monitoring](https://mlsanity.com/paper/2207.14550/) (2022)
- [Improved Best-of-Both-Worlds Guarantees for Multi-Armed Bandits: FTRL with General Regularizers and Multiple Optimal Arms](https://mlsanity.com/paper/2302.13534/) (2023)
- [A Near-Optimal Best-of-Both-Worlds Algorithm for Online Learning with Feedback Graphs](https://mlsanity.com/paper/2206.00557/) (2022)
- [Cleaning up the neighborhood: A full classification for adversarial partial monitoring](https://mlsanity.com/paper/1805.09247/) (2018)
- [Stability-penalty-adaptive follow-the-regularized-leader: Sparsity, game-dependency, and best-of-both-worlds](https://mlsanity.com/paper/2305.17301/) (2023)
- [Adversarially Robust Multi-Armed Bandit Algorithm with Variance-Dependent Regret Bounds](https://mlsanity.com/paper/2206.06810/) (2022)
- [Regret Lower Bound and Optimal Algorithm in Finite Stochastic Partial Monitoring](https://mlsanity.com/paper/1509.09011/) (2015)
- [Analysis and Design of Thompson Sampling for Stochastic Partial Monitoring](https://mlsanity.com/paper/2006.09668/) (2020)

## Built on by (most cited first, 3 of 3)

- [A Simple and Adaptive Learning Rate for FTRL in Online Learning with Minimax Regret of Theta(T2/3) and its Application to Best-of-Both-Worlds](https://mlsanity.com/paper/2405.20028/) (2024)
- [Revisiting Follow-the-Perturbed-Leader with Unbounded Perturbations in Bandit Problems](https://mlsanity.com/paper/2508.18604/) (2025)
- [Instance-Dependent Regret Bounds for Nonstochastic Linear Partial Monitoring](https://mlsanity.com/paper/2510.19158/) (2025)

## Abstract (arXiv)

Partial monitoring is a generic framework of online decision-making problems with limited feedback. To make decisions from such limited feedback, it is necessary to find an appropriate distribution for exploration. Recently, a powerful approach for this purpose, exploration by optimization (ExO), was proposed, which achieves optimal bounds in adversarial environments with follow-the-regularized-leader for a wide range of online decision-making problems. However, a naive application of ExO in stochastic environments significantly degrades regret bounds. To resolve this issue in locally observable games, we first establish a new framework and analysis for ExO with a hybrid regularizer. This development allows us to significantly improve existing regret bounds of best-of-both-worlds (BOBW) algorithms, which achieves nearly optimal bounds both in stochastic and adversarial environments. In particular, we derive a stochastic regret bound of O(suma neq a^* k2 m2 log T / Deltaa), where k, m, and T are the numbers of actions, observations and rounds, a^* is an optimal action, and Deltaa is the suboptimality gap for action a. This bound is roughly Theta(k2 log T) times smaller than existing BOBW bounds. In addition, for globally observable games, we provide a new BOBW algorithm with the first O(log T) stochastic bound.