Pablo Samuel Castro
Research Areas
Authored Publications
Sort By
Bigger, Better, Faster: Human-level Atari with human-level efficiency
Max Schwarzer
Johan Obando Ceron
Aaron Courville
Marc Bellemare
ICML (2023)
Preview abstract
We introduce a value-based RL agent, which we call BBF, that achieves super-human performance in the Atari 100K benchmark. BBF relies on scaling the neural networks used for value estimation, as well as a number of other design choices that enable this scaling in a sample-efficient manner. We conduct extensive analyses of these design choices and provide insights for future work. We end with a discussion about moving the goalpost for sample-efficient RL research on the ALE.
View details
Offline Reinforcement Learning with On-Policy Q-Function Regularization
Laixi Shi
Yuejie Chi
Matthieu Geist
European Conference on Machine Learning (ECML) (2023)
Preview abstract
The core challenge of offline reinforcement learning (RL) is dealing with the (potentially catastrophic) extrapolation error induced by the distribution shift between the history dataset and the desired policy. A large portion of prior work tackles this challenge by implicitly/explicitly regularizing the learning policy towards the behavior policy, which
is hard to estimate reliably in practice. In this work, we propose to regularize towards the Q-function of the behavior policy instead of the behavior policy itself, under the premise that the Q-function can be estimated more reliably and easily by a SARSA-style estimate and handles the extrapolation error more straightforwardly. We propose two algorithms taking advantage of the estimated Q-function through regularizations, and demonstrate they exhibit strong performance on the D4RL benchmarks.
View details
Proto-Value Networks: Scaling Representation Learning with Auxiliary Tasks
Jesse Farebrother
Joshua Greaves
Charline Le Lan
Marc Bellemare
International Conference on Learning Representations (ICLR) (2023)
Preview abstract
Auxiliary tasks improve the representations learned by deep reinforcement learning agents. Analytically, their effect is reasonably well-understood; in practice, how-ever, their primary use remains in support of a main learning objective, rather than as a method for learning representations. This is perhaps surprising given that many auxiliary tasks are defined procedurally, and hence can be treated as an essentially infinite source of information about the environment. Based on this observation, we study the effectiveness of auxiliary tasks for learning rich representations, focusing on the setting where the number of tasks and the size of the agent’s network are simultaneously increased. For this purpose, we derive a new family of auxiliary tasks based on the successor measure. These tasks are easy to implement and have appealing theoretical properties. Combined with a suitable off-policy learning rule, the result is a representation learning algorithm that can be understood as extending Mahadevan & Maggioni (2007)’s proto-value functions to deep reinforcement learning – accordingly, we call the resulting object proto-value networks. Through a series of experiments on the Arcade Learning Environment, we demonstrate that proto-value networks produce rich features that may be used to obtain performance comparable to established algorithms, using only linear approximation and a small number (~4M) of interactions with the environment’s reward function.
View details
Preview abstract
Behavioural metrics have been shown to be an effective mechanism for constructing representations in reinforcement learning. We present a novel perspective on
behavioural metrics for Markov decision processes via the use of positive definite
kernels. We leverage this new perspective to define a new metric that is provably
equivalent to the recently introduced MICo distance (Castro et al., 2021). The kernel perspective further enables us to provide new theoretical results, which has so far
eluded prior work. These include bounding value function differences by means of
our metric, and the demonstration that our metric can be provably embedded into a
finite-dimensional Euclidean space with low distortion error. These are two crucial
properties when using behavioural metrics for reinforcement learning representations. We complement our theory with strong empirical results that demonstrate
the effectiveness of these methods in practice.
View details
Reincarnating Reinforcement Learning: Reusing Prior Computation to Accelerate Progress
Max Allen Schwarzer
Aaron Courville
Marc G. Bellemare
NeurIPS (2022)
Preview abstract
Learning tabula rasa, that is without any prior knowledge, is the prevalent workflow in reinforcement learning (RL) research. However, RL systems, when applied to large-scale settings, rarely operate tabula rasa. Such large-scale systems undergo multiple design or algorithmic changes during their development cycle and use ad hoc approaches for incorporating these changes without re-training from scratch, which would have been prohibitively expensive. Additionally, the inefficiency of deep RL typically excludes researchers without access to industrial-scale resources from tackling computationally-demanding problems. To address these issues, we present reincarnating RL as an alternative workflow or class of problem settings, where prior computational work (e.g., learned policies) is reused or transferred between design iterations of an RL agent, or from one RL agent to another. As a step towards enabling reincarnating RL from any agent to any other agent, we focus on the specific setting of efficiently transferring an existing sub-optimal policy to a standalone value-based RL agent. We find that existing approaches fail in this setting and propose a simple algorithm to address their limitations. Equipped with this algorithm, we demonstrate reincarnating RL's gains over tabula rasa RL on Atari 2600 games, a challenging locomotion task, and the real-world problem of navigating stratospheric balloons. Overall, this work argues for an alternative approach to RL research, which we believe could significantly improve real-world RL adoption and help democratize it further. Open-sourced code and trained agents at
View details
The State of Sparse Training in Deep Reinforcement Learning
Erich Elsen
Proceedings of the 39th International Conference on Machine Learning, PMLR (2022)
Preview abstract
The use of sparse neural networks has seen a rapid growth in recent years, particularly in computer vision; their appeal stems largely due to the reduced number of parameters required to train and store, as well as in an increase in learning efficiency. Somewhat surprisingly, there have been very few efforts exploring their use in deep reinforcement learning (DRL). In this work we perform a systematic investigation into applying a number of existing sparse training techniques on a variety of DRL agents and environments. Our results highlight the overall challenge that reinforcement learning poses for sparse training methods, complemented by detailed analyses on how the various components in DRL are affected by the use of sparse networks. We conclude by suggesting some promising avenues for improving the effectiveness of general sparse training methods, as well as for advancing their use in DRL.
View details
A general class of surrogate functions for stable and efficient reinforcement learning
Sharan Vaswani
Simone Totaro
Robert Müller
Shivam Garg
Matthieu Geist
Marlos C. Machado
Nicolas Le Roux
AISTATS (2022)
Preview abstract
Common policy gradient methods rely on the maximization of a sequence of surrogate functions. In recent years, many such surrogate functions have been proposed, most without strong theoretical guarantees, leading to algorithms such as TRPO, PPO, or MPO. Rather than design yet another surrogate function, we instead propose a general framework (FMA-PG) based on functional mirror ascent that gives rise to an entire family of surrogate functions. We construct surrogate functions that enable policy improvement guarantees, a property not shared by most existing surrogate functions. Crucially, these guarantees hold regardless of the choice of policy parameterization. Moreover, a particular instantiation of FMA-PG recovers important implementation heuristics (e.g., using forward vs reverse KL divergence) resulting in a variant of TRPO with additional desirable properties. Via experiments on simple reinforcement learning problems, we evaluate the algorithms instantiated by FMA-PG. The proposed framework also suggests an improved variant of PPO, whose robustness and efficiency we empirically demonstrate on the MuJoCo suite.
View details
Preview abstract
Reinforcement learning techniques are being applied to increasingly larger systems where it becomes untenable to maintain direct estimates for
individual states, in particular for continuous-state
systems. Instead, researchers often leverage state
similarity (whether implicitly or explicitly) to
build models that can generalize well from a limited set of samples. The notion of state similarity
used is thus of crucial importance, as it will directly affect the quality of the approximations
and performance of the algorithms. Indeed, there
have been a number of works that investigate –
both on a theoretical and an empirical basis – how
best to construct these neighborhoods and topologies. However, the choice of metric is not always
clear and is often not fully specified when new
algorithms are introduced. In this paper we aim
to clarify the landscape of existing metrics and
provide guidelines for the choice of metric when
designing or implementing algorithms. We do this
by first introducing a unified formalism for specifying these topologies, through the lens of metrics
or distance measures, and clarify the relationship
between them. We establish a hierarchy amongst
the different metrics and their theoretical implications on the Markov Decision Process (MDP)
specifying the reinforcement learning problem.
We complement our theoretical results with empirical evaluations showcasing the differences between the metrics considered.
View details
Preview abstract
Offline reinforcement learning, which uses observational data instead of active environmental interaction, has been shown to be a challenging problem. Recent solutions typically involve constraints on the learner’s policy, preventing strong deviations from the state-action distribution of the dataset. Although the suggested methods are evaluated using non-linear function approximation, their theoretical justifications are mostly limited to the tabular or linear cases. Given the impressive results of deep reinforcement learning, we argue for a clearer understanding of the challenges in this setting.
In the vein of Held & Hein's classic 1963 experiment, we propose “tandem learning”, an experimental paradigm which facilitates our in-depth empirical analysis of the difficulties in offline reinforcement learning. We identify function approximation in conjunction with inadequate data distributions as the strongest factors, thereby extending but also challenging certain assumptions made in past work. Our results provide a more principled view, and new insights on potential directions for future work on offline reinforcement learning.
View details
Deep Reinforcement Learning at the Edge of the Statistical Precipice
Max Schwarzer
Aaron Courville
Marc G. Bellemare
Advances in Neural Information Processing Systems (2021)
Preview abstract
Deep reinforcement learning (RL) algorithms are predominantly evaluated by comparing their relative performance on a large suite of tasks. Most published results on deep RL benchmarks compare point estimates of aggregate performance such as mean and median scores across tasks, ignoring the statistical uncertainty implied by the use of a finite number of training runs. Beginning with the Arcade Learning Environment (ALE), the shift towards computationally-demanding benchmarks has led to the practice of evaluating only a small number of runs per task, exacerbating the statistical uncertainty in point estimates. In this paper, we argue that reliable evaluation in the few run deep RL regime cannot ignore the uncertainty in results without running the risk of slowing down progress in the field. We illustrate this point using a case study on the Atari 100k benchmark, where we find substantial discrepancies between conclusions drawn from point estimates alone versus a more thorough statistical analysis. With the aim of increasing the field's confidence in reported results with a handful of runs, we advocate for reporting interval estimates of aggregate performance and propose performance profiles to account for the variability in results, as well as present more robust and efficient aggregate metrics, such as interquartile mean scores, to achieve small uncertainty in results. Using such statistical tools, we scrutinize performance evaluations of existing algorithms on other widely used RL benchmarks including the ALE, Procgen, and the DeepMind Control Suite, again revealing discrepancies in prior comparisons. Our findings call for a change in how we evaluate performance in deep RL, for which we present a more rigorous evaluation methodology, accompanied with an open-source library rliable, to prevent unreliable results from stagnating the field. See agarwl.github.io/rliable for more details.
View details
