Learning Abstract Models for Long-Horizon Exploration
Authors: Evan Zheran Liu, Ramtin Keramati, Sudarshan Seshadri, Kelvin Guu, Panupong Pasupat, Emma Brunskill, Percy Liang
Keywords: Reinforcement Learning, Hierarchical Reinforcement Learning, Model-based Reinforcement Learning, Exploration
TL;DR: We automatically construct and explore a small abstract Markov Decision Process, enabling us to achieve state-of-the-art results on Montezuma's Revenge, Pitfall!, and Private Eye by a significant margin.
Abstract: In high-dimensional reinforcement learning settings with sparse rewards, performing
effective exploration to even obtain any reward signal is an open challenge.
While model-based approaches hold promise of better exploration via planning, it
is extremely difficult to learn a reliable enough Markov Decision Process (MDP)
in high dimensions (e.g., over 10^100 states). In this paper, we propose learning
an abstract MDP over a much smaller number of states (e.g., 10^5), which we can
plan over for effective exploration. We assume we have an abstraction function
that maps concrete states (e.g., raw pixels) to abstract states (e.g., agent position,
ignoring other objects). In our approach, a manager maintains an abstract
MDP over a subset of the abstract states, which grows monotonically through targeted
exploration (possible due to the abstract MDP). Concurrently, we learn a
worker policy to travel between abstract states; the worker deals with the messiness
of concrete states and presents a clean abstraction to the manager. On three of
the hardest games from the Arcade Learning Environment (Montezuma's,
Pitfall!, and Private Eye), our approach outperforms the previous
state-of-the-art by over a factor of 2 in each game. In Pitfall!, our approach is
the first to achieve superhuman performance without demonstrations.