Kernel-Based Decentralized Policy Evaluation for Reinforcement Learning.

We investigate the decentralized nonparametric policy evaluation problem within reinforcement learning (RL), focusing on scenarios where multiple agents collaborate to learn the state-value function using sampled state transitions and privately observed rewards. Our approach centers on a regression-based multistage iteration technique employing infinite-dimensional gradient descent (GD) within a reproducing kernel Hilbert space (RKHS). To make computation and communication more feasible, we employ Nyström approximation to project this space into a finite-dimensional one. We establish statistical error bounds to describe the convergence of value function estimation, marking the first instance of such analysis within a fully decentralized nonparametric framework. We compare the regression-based method to the kernel temporal difference (TD) method in some numerical studies.