64 research outputs found
Improving Exploration in Evolution Strategies for Deep Reinforcement Learning via a Population of Novelty-Seeking Agents
Evolution strategies (ES) are a family of black-box optimization algorithms
able to train deep neural networks roughly as well as Q-learning and policy
gradient methods on challenging deep reinforcement learning (RL) problems, but
are much faster (e.g. hours vs. days) because they parallelize better. However,
many RL problems require directed exploration because they have reward
functions that are sparse or deceptive (i.e. contain local optima), and it is
unknown how to encourage such exploration with ES. Here we show that algorithms
that have been invented to promote directed exploration in small-scale evolved
neural networks via populations of exploring agents, specifically novelty
search (NS) and quality diversity (QD) algorithms, can be hybridized with ES to
improve its performance on sparse or deceptive deep RL tasks, while retaining
scalability. Our experiments confirm that the resultant new algorithms, NS-ES
and two QD algorithms, NSR-ES and NSRA-ES, avoid local optima encountered by ES
to achieve higher performance on Atari and simulated robots learning to walk
around a deceptive trap. This paper thus introduces a family of fast, scalable
algorithms for reinforcement learning that are capable of directed exploration.
It also adds this new family of exploration algorithms to the RL toolbox and
raises the interesting possibility that analogous algorithms with multiple
simultaneous paths of exploration might also combine well with existing RL
algorithms outside ES
ES Is More Than Just a Traditional Finite-Difference Approximator
An evolution strategy (ES) variant based on a simplification of a natural
evolution strategy recently attracted attention because it performs
surprisingly well in challenging deep reinforcement learning domains. It
searches for neural network parameters by generating perturbations to the
current set of parameters, checking their performance, and moving in the
aggregate direction of higher reward. Because it resembles a traditional
finite-difference approximation of the reward gradient, it can naturally be
confused with one. However, this ES optimizes for a different gradient than
just reward: It optimizes for the average reward of the entire population,
thereby seeking parameters that are robust to perturbation. This difference can
channel ES into distinct areas of the search space relative to gradient
descent, and also consequently to networks with distinct properties. This
unique robustness-seeking property, and its consequences for optimization, are
demonstrated in several domains. They include humanoid locomotion, where
networks from policy gradient-based reinforcement learning are significantly
less robust to parameter perturbation than ES-based policies solving the same
task. While the implications of such robustness and robustness-seeking remain
open to further study, this work's main contribution is to highlight such
differences and their potential importance
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