Book Image

TensorFlow Reinforcement Learning Quick Start Guide

By : Kaushik Balakrishnan
Book Image

TensorFlow Reinforcement Learning Quick Start Guide

By: Kaushik Balakrishnan

Overview of this book

Advances in reinforcement learning algorithms have made it possible to use them for optimal control in several different industrial applications. With this book, you will apply Reinforcement Learning to a range of problems, from computer games to autonomous driving. The book starts by introducing you to essential Reinforcement Learning concepts such as agents, environments, rewards, and advantage functions. You will also master the distinctions between on-policy and off-policy algorithms, as well as model-free and model-based algorithms. You will also learn about several Reinforcement Learning algorithms, such as SARSA, Deep Q-Networks (DQN), Deep Deterministic Policy Gradients (DDPG), Asynchronous Advantage Actor-Critic (A3C), Trust Region Policy Optimization (TRPO), and Proximal Policy Optimization (PPO). The book will also show you how to code these algorithms in TensorFlow and Python and apply them to solve computer games from OpenAI Gym. Finally, you will also learn how to train a car to drive autonomously in the Torcs racing car simulator. By the end of the book, you will be able to design, build, train, and evaluate feed-forward neural networks and convolutional neural networks. You will also have mastered coding state-of-the-art algorithms and also training agents for various control problems.
Table of Contents (11 chapters)

Learning PPO

PPO is an extension to TRPO, and was introduced in 2017 by researchers at OpenAI. PPO is also an on-policy algorithm, and can be applied to discrete action problems as well as continuous actions. It uses the same ratio of policy distributions as in TRPO, but does not use the KL divergence constraint. Specifically, PPO uses three loss functions that are combined into one. We will now see the three loss functions.

PPO loss functions

The first of the three loss functions involved in PPO is called the clipped surrogate objective. Let rt(θ) denote the ratio of the new to old policy probability distributions:

The clipped surrogate objective is given by the following equation, where At is the advantage function...