Abstract

ABSTRACTPolicy search algorithms have facilitated application of Reinforcement Learning (RL) to dynamic systems, such as control of robots. Many policy search algorithms are based on the policy gradient, and thus may suffer from slow convergence or local optima complications. In this paper, we take a Bayesian approach to policy search under RL paradigm, for the problem of controlling a discrete time Markov decision process with continuous state and action spaces and with a multiplicative reward structure. For this purpose, we assume a prior over policy parameters and aim for the ‘posterior’ distribution where the ‘likelihood’ is the expected reward. We propound a Markov chain Monte Carlo algorithm as a method of generating samples for policy parameters from this posterior. The proposed algorithm is compared with certain well-known policy gradient-based RL methods and exhibits more appropriate performance in terms of time response and convergence rate, when applied to a nonlinear model of a Cart-Pole benchmark.

Highlights

  • Reinforcement learning (RL) can be considered as a topic of interest among the researchers in the field of machine learning, control and robotics; see Sutton and Barto (1998) for an introduction

  • We considered the control problem of an Markov decision processes (MDP) with continuous state and action spaces in finite time horizon and presented a novel policy search method for a class of parameterized polices in RL under a Bayesian learning framework

  • The proposed learning approach is an MCMC algorithm that uses estimates of the expected multiplicative total reward which are attained with an sequential Monte Carlo (SMC) algorithm

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Summary

A Markov chain Monte Carlo algorithm for Bayesian policy search

SYSTEMS SCIENCE & CONTROL ENGINEERING: AN OPEN ACCESS JOURNAL 2018, VOL. Vahid Tavakol Aghaeia, Ahmet Onata and Sinan Yıldırımb aFaculty of Engineering and Natural Sciences, Mechatronics Engineering, Sabancı University, Istanbul, Turkey; bFaculty of Engineering and Natural Sciences, Industrial Engineering, Sabancı University, Istanbul, Turkey

Introduction
Markov decision processes
Reward-based policy search
Gradient-based algorithms for policy optimization
A Bayesian framework for RL
MCMC for policy search
The inverted pendulum model
Simulations
Numerical experiments
Findings
Conclusion and future work

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