Adaptive Environment Design for Robust Inverse Reinforcement Learning

Core Concepts

By adaptively designing a sequence of demonstration environments, the learner can recover a more robust and informative estimate of the unknown reward function compared to learning from a fixed environment or random environment variations.

Abstract

The paper presents a framework for Environment Design for Inverse Reinforcement Learning (ED-BIRL), where the learner adaptively selects a sequence of demonstration environments for the human expert to act in. This is in contrast to prior work that has focused on improving existing Inverse Reinforcement Learning (IRL) algorithms directly.
The key idea is that by carefully curating the set of environments the expert demonstrates the task in, the learner can improve the sample-efficiency and robustness of the learned reward function. The authors formalize this environment design process as a minimax Bayesian regret objective, which aims to select environments that maximize the regret of the regret-minimizing policy. This ensures that the learner discovers all performance-relevant aspects of the unknown reward function.
The authors also extend Bayesian IRL methods to handle expert demonstrations across multiple environments. They provide an efficient algorithm for computing the maximin environment when the set of environments has a useful structure, allowing the learner to explore the space of environments effectively.
Experiments on maze navigation and randomly generated MDPs demonstrate that ED-BIRL can recover the true reward function and learn more robust reward estimates compared to learning from a fixed environment or random environment variations.

Stats

The true reward function yields reward 1 in goal states and reward -1 in lava states.
The maximum amount of variation in the demo environments is ρdemo = 0.5.
The maximum amount of variation in the test environments is ρtest = 0.5.

Quotes

"By adaptively designing a sequence of demo environments, we aim to improve the sample-efficiency of IRL methods and the robustness of learned rewards against variations in the environment dynamics."
"Our hypothesis is that intelligently choosing such demo environments will allow us to improve the sample-efficiency of IRL methods and the robustness of learned rewards against variations in the environment dynamics."

Key Insights Distilled From

Environment Design for Inverse Reinforcement Learning

by Thomas Klein... at arxiv.org 05-07-2024

https://arxiv.org/pdf/2210.14972.pdf

Deeper Inquiries

How can the environment design process be extended to settings with multiple human experts, each with their own preferences or biases?

In the context of multiple human experts with varying preferences or biases, the environment design process can be extended by incorporating a mechanism to account for the diversity in expert behavior. One approach could involve creating a personalized environment for each expert based on their demonstrated trajectories and preferences. This personalized environment could be tailored to challenge the specific skills or behaviors of each expert, allowing them to showcase their expertise in a setting that aligns with their individual preferences.
Additionally, the environment design process could incorporate a collaborative or competitive element where experts interact with each other in shared or adversarial environments. By observing how experts respond to each other's actions, the learner can gain insights into their unique strategies and preferences. This collaborative setting can lead to a more comprehensive understanding of the experts' behaviors and enable the learner to design environments that cater to a diverse range of preferences and biases.
Furthermore, the environment design process can leverage techniques from multi-agent reinforcement learning to model interactions between multiple experts and adaptively adjust the environments based on the collective behavior of the experts. By considering the interactions and dynamics between experts, the learner can create environments that not only accommodate individual preferences but also foster collaboration, competition, or cooperation among the experts.

What are the limitations of the minimax Bayesian regret objective, and are there alternative objectives that could be explored for environment design?

While the minimax Bayesian regret objective offers a principled approach to environment design in inverse reinforcement learning, it has certain limitations that may impact its effectiveness in practice. One limitation is the computational complexity associated with finding the maximin environment, especially in settings with a large or continuous space of possible environments. The search for the maximin environment may become infeasible or require significant computational resources, limiting the scalability of the approach.
Another limitation is the assumption of a fixed prior distribution over reward functions, which may not accurately capture the true uncertainty in the reward estimation process. In dynamic environments or with evolving expert behaviors, the fixed prior may not adapt well to changing conditions, leading to suboptimal environment design decisions.
Alternative objectives that could be explored for environment design include entropy-based approaches, where the goal is to maximize the entropy of the learned reward distribution. By maximizing entropy, the learner can encourage exploration and diversity in the learned reward functions, potentially leading to more robust and generalizable solutions. Additionally, objectives based on information gain or uncertainty reduction could be considered to actively seek informative environments that provide the most valuable information for reward learning.

Can the ideas presented in this work be applied to other inverse problems beyond reinforcement learning, such as inverse optimal control or inverse planning?

Yes, the ideas presented in this work on environment design for inverse reinforcement learning can be extended to other inverse problems beyond reinforcement learning, such as inverse optimal control or inverse planning. The concept of adaptively designing environments to elicit informative demonstrations from an expert can be applied to various inverse problems where the learner seeks to infer a latent function or model from observed data.
In the context of inverse optimal control, the environment design process can involve creating scenarios or tasks that challenge the expert to demonstrate their optimal control strategies. By designing environments that highlight specific aspects of the optimal control policy, the learner can learn the underlying reward or cost function governing the expert's behavior.
Similarly, in inverse planning, the environment design approach can be used to construct problem instances or scenarios that reveal the decision-making process of the expert planner. By carefully curating environments that require the expert to make strategic decisions, the learner can infer the underlying planning objectives or preferences of the expert.
Overall, the principles of adaptive environment design for eliciting expert demonstrations can be generalized to a wide range of inverse problems, providing a systematic and efficient way to learn from human expertise in various domains beyond reinforcement learning.