Harley Wiltzer

A Distributional Analogue to the Successor Representation

Harley Wiltzer

Jesse Farebrother

Arthur Gretton

Yunhao Tang

Andre Barreto

Will Dabney

Bellemare Marc-Emmanuel

Mark Rowland

This paper contributes a new approach for distributional reinforcement learning which elucidates a clean separation of transition structure … (see more)and reward in the learning process. Analogous to how the successor representation (SR) describes the expected consequences of behaving according to a given policy, our distributional successor measure (SM) describes the distributional consequences of this behaviour. We formulate the distributional SM as a distribution over distributions and provide theory connecting it with distributional and model-based reinforcement learning. Moreover, we propose an algorithm that learns the distributional SM from data by minimizing a two-level maximum mean discrepancy. Key to our method are a number of algorithmic techniques that are independently valuable for learning generative models of state. As an illustration of the usefulness of the distributional SM, we show that it enables zero-shot risk-sensitive policy evaluation in a way that was not previously possible.

2024-07-22

International Conference on Machine Learning (Accept (Spotlight))

doi.org

proceedings.mlr.press

Policy Optimization in a Noisy Neighborhood: On Return Landscapes in Continuous Control

Bellemare Marc-Emmanuel

Deep reinforcement learning agents for continuous control are known to exhibit significant instability in their performance over time. In th… (see more)is work, we provide a fresh perspective on these behaviors by studying the return landscape: the mapping between a policy and a return. We find that popular algorithms traverse noisy neighborhoods of this landscape, in which a single update to the policy parameters leads to a wide range of returns. By taking a distributional view of these returns, we map the landscape, characterizing failure-prone regions of policy space and revealing a hidden dimension of policy quality. We show that the landscape exhibits surprising structure by finding simple paths in parameter space which improve the stability of a policy. To conclude, we develop a distribution-aware procedure which finds such paths, navigating away from noisy neighborhoods in order to improve the robustness of a policy. Taken together, our results provide new insight into the optimization, evaluation, and design of agents.

2023-12-11

Conference on Neural Information Processing Systems (Accept (poster))

doi.org

openreview.net

Distributional Hamilton-Jacobi-Bellman Equations for Continuous-Time Reinforcement Learning

Harley Wiltzer

David Meger

Bellemare Marc-Emmanuel

Continuous-time reinforcement learning offers an appealing formalism for describing control problems in which the passage of time is not nat… (see more)urally divided into discrete increments. Here we consider the problem of predicting the distribution of returns obtained by an agent interacting in a continuous-time, stochastic environment. Accurate return predictions have proven useful for determining optimal policies for risk-sensitive control, learning state representations, multiagent coordination, and more. We begin by establishing the distributional analogue of the Hamilton-Jacobi-Bellman (HJB) equation for Itô diffusions and the broader class of Feller-Dynkin processes. We then specialize this equation to the setting in which the return distribution is approximated by

2022-07-18

International Conference on Machine Learning (Accept for Short Presentation)

doi.org

proceedings.mlr.press

Revisiting Successor Features for Inverse Reinforcement Learning

Sanjiban Choudhury

2019-12-31