Counting Reward Automata: Sample Efficient Reinforcement Learning Through The Exploitation of Reward Function Structure

Tristan Bester, Benjamin Rosman, Steven James, Geraud Nangue Tasse

Keywords: Neuro-Symbolic Learning, Formal Languages and Automata, Reinforcement Learning, Deep Learning

TL;DR: We model the reward function in reinforcement learning though the use of finite state machines to increase sample efficiency.

Abstract: We present counting reward automata-a finite state machine variant capable of modelling any reward function expressible as a formal language. Unlike previous approaches, which are limited to the expression of tasks as regular languages, our framework allows for tasks described by unrestricted grammars. We prove that an agent equipped with such an abstract machine is able to solve a larger set of tasks than those utilising current approaches. We show that this increase in expressive power does not come at the cost of increased automaton complexity. A selection of learning algorithms are presented which exploit automaton structure to improve sample efficiency. We show that the state machines required in our formulation can be specified from natural language task descriptions using large language models. Empirical results demonstrate that our method outperforms competing approaches in terms of sample efficiency, automaton complexity, and task completion.

Submission Number: 10