Reparameterized Policy Learning for Multimodal Trajectory Optimization
Zhiao Huang Litian Liang Zhan Ling Xuanlin Li Chuang Gan Hao Su
We investigate the challenge of parametrizing policies for reinforcement
learning (RL) in high-dimensional continuous action spaces. Our objective is to
develop a multimodal policy that overcomes limitations inherent in the
commonly-used Gaussian parameterization. To achieve this, we propose a
principled framework that models the continuous RL policy as a generative model
of optimal trajectories. By conditioning the policy on a latent variable, we
derive a novel variational bound as the optimization objective, which promotes
exploration of the environment. We then present a practical model-based RL
method, called Reparameterized Policy Gradient (RPG), which leverages the
multimodal policy parameterization and learned world model to achieve strong
exploration capabilities and high data efficiency. Empirical results
demonstrate that our method can help agents evade local optima in tasks with
dense rewards and solve challenging sparse-reward environments by incorporating
an object-centric intrinsic reward. Our method consistently outperforms
previous approaches across a range of tasks. Code and supplementary materials
are available on the project page https://haosulab.github.io/RPG/