Reinforcement Learning
Review for NeurIPS paper: A Unified Switching System Perspective and Convergence Analysis of Q-Learning Algorithms
The paper provides a new tool (theory of switching systems) for the convergence analysis of RL algorithms that can be of interest to the wider RL theory community. Compared with existing results, several improvements are made. Authors should revise the paper to address reviewer comments. Prior works in this area need to be discussed more carefully, as pointed out by reviewers.
Reviews: Finite-Time Performance Bounds and Adaptive Learning Rate Selection for Two Time-Scale Reinforcement Learning
Here are few suggestions for expanding your presentation: 1. The literature review needs to be broadened. In particular, you should discuss the work of Liu et al., JAIR 2019 (Proximal Gradient TD Learning), which analyzes two time-scale algorithms that include a proximal gradient step. The results in that paper show improved finite sample bounds over classic gradient TD methods, like GTD2. How do your results compare with those in that paper, and in particular, can your analysis be extended to GTD2-MP (the mirror-prox variant of GTD2, which has an improved finite sample convergence rate compared to GTD2. 2. Two time scale algorithms are somewhat more complex than the standard TD method, and Sutton et al. and others have developed a variant of TD called emphatic TD (JMLR 2016: "An Emphatic Approach to the Problem of Off-policy Temporal-Difference Learning") that is stable under off-policy training.
Reviews: Generalization in Reinforcement Learning with Selective Noise Injection and Information Bottleneck
This work builds on the previous work about generalization in RL ([10] in the paper references) by (re-)investigating the classical stochastic regularization approaches in this context. It completes and updates the claims made in [10] by focusing of similar performance based experiments. Clarity: The method is clearly described in the paper. Significance: The question of generalization in RL is of great interest to the field. Main comments: - The paper motivates well the problems one faces when is comes to regularization in RL.
Reviews: Generalization in Reinforcement Learning with Selective Noise Injection and Information Bottleneck
According to the reviews, this submission is quite easy to evaluate. All reviewers view the paper as presenting a novel and promising technique for regularization via noise injection along with variational information bottleneck. Performance benefits are also shown by state-of-art performance in the CoinRunner domain. Reviewers also found the author feedback quite convincing, as two of the three reviewers raised their overall scores. There were only a few issues mentioned in the revised reviews, and these issues were considered as minor.
Reviews: Characterizing the Exact Behaviors of Temporal Difference Learning Algorithms Using Markov Jump Linear System Theory
Summary: - The main contribution of the paper is to write the TD update as a MJLS over an augmented parameter space with one parameter vector for each pair of states in the underlying MDP. - After presenting MJLS and the idea of the augmented parameter space, they first consider the IID case where pairs of states are chosen IID and give formulas for the expected error and its covariance. Under an additional ergodicity assumption they give a convergence rate to limiting quantities. For small learning rates (not exactly clear how small in terms of problem parameters) a perturbation analysis gives an estimate of what this convergence rate is (although the value of lambda_{max real} \bar A remains unclear in terms of the parameters of the problem). Pros: - The originality of the connection between TD dynamics and MJLS is a good contribution that could increase the flow of ideas from control theory to RL. In addition, the formulation of the augmented state space seems to be a potentially useful analysis tool.
Reviews: Characterizing the Exact Behaviors of Temporal Difference Learning Algorithms Using Markov Jump Linear System Theory
This paper provides an analysis of Temporal-Difference algorithms using the theory of Markov Jump Linear Systems (MJLS). Its main contributions are to establish exact dynamics for the first and second order TD moments using linear function approximation, given by Linear Time Invariant systems. Reviewers found the technical contributions of this paper to be very strong, with potentially important significance in the study of a central object in RL such as TD learning. The main point of contention is the current presentation, which is cumbersome with notation, with page-long theorem statements, and, most importantly, without sufficient discussion of how these results relate to existing work on the convergence analysis of TD learning. However, after careful discussion with reviewers and having read the author feedback (which does promise to improve readability), considered that the positive contributions outweight the risk of poor readibility, and recommends acceptance, urging the authors to address the concerns raised by reviewers and AC.
Review for NeurIPS paper: Upper Confidence Primal-Dual Reinforcement Learning for CMDP with Adversarial Loss
Weaknesses: (W1): As such the high-level outline of the proof strategy follows previous procedures for drift analysis in (Yu et al. 2017) and MDP analysis in (Neu et al. 2012 and Rosenberg et al. 2019). Lemma B.2 is very similar to Lemma 4 in Neu et al. 2012 and Lemma B.2 in Rosenberg et al. 2019. Lemma 5.2 mirrors Lemma 8 in Yu et al. 2017. Technical lemmas for stochastic analysis are also from the previous paper: (Lemma B.6 and B.7 are Lemma 5 and 9 in Yu et al. 2017). The main lemma, Lemma 5.3, has the same goal as Lemma 7 in Yu et al. 2017, which is to show Q_t satisfies the drift condition stated in Lemma 5 in Yu et al. 2017. Lemma 5.6 is also exact as Lemma 3 in Yu et al. 2017.
Review for NeurIPS paper: Upper Confidence Primal-Dual Reinforcement Learning for CMDP with Adversarial Loss
I want to thank the authors for preparing the detailed rebuttal. This paper was discussed among all the reviewers during the post-rebuttal discussion phase. Overall, the reviewers are excited about this work on solving constrained MDP problems and have a positive assessment of the paper. All the reviewers acknowledged the theoretical contributions, especially in a challenging setting with unknown dynamics and non-stationary loss function. There was a clear consensus that the paper should be accepted.
Review for NeurIPS paper: Meta-Gradient Reinforcement Learning with an Objective Discovered Online
Strengths: The idea of formulating the inner loss for meta RL as learning from the objective discovered by its own is interesting and novel. Generally, defining the algorithm to self-discover its objective makes the learning algorithm moves one step closer towards developing automated machine intelligence compared to the conventional meta RL methods which greatly rely on expert's design choice such as the hyperparameter to perform learning-to-learn. The authors present extensive experiment results to evaluate the proposed method. The proposed method has been evaluated on three task domains: a catch game to demonstrate the method could effectively learn bootstrapping, a 5-state random walk to demonstrate the method works in non-stationary environments, and ALE which is a large-scale RL testbed. In all the task domains, the proposed method achieves noticeable performance improvement over the compared baselines.