Book Image

Deep Reinforcement Learning Hands-On - Second Edition

By : Maxim Lapan
Book Image

Deep Reinforcement Learning Hands-On - Second Edition

By: Maxim Lapan

Overview of this book

Deep Reinforcement Learning Hands-On, Second Edition is an updated and expanded version of the bestselling guide to the very latest reinforcement learning (RL) tools and techniques. It provides you with an introduction to the fundamentals of RL, along with the hands-on ability to code intelligent learning agents to perform a range of practical tasks. With six new chapters devoted to a variety of up-to-the-minute developments in RL, including discrete optimization (solving the Rubik's Cube), multi-agent methods, Microsoft's TextWorld environment, advanced exploration techniques, and more, you will come away from this book with a deep understanding of the latest innovations in this emerging field. In addition, you will gain actionable insights into such topic areas as deep Q-networks, policy gradient methods, continuous control problems, and highly scalable, non-gradient methods. You will also discover how to build a real hardware robot trained with RL for less than $100 and solve the Pong environment in just 30 minutes of training using step-by-step code optimization. In short, Deep Reinforcement Learning Hands-On, Second Edition, is your companion to navigating the exciting complexities of RL as it helps you attain experience and knowledge through real-world examples.
Table of Contents (28 chapters)
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Index

The REINFORCE method

The formula of policy gradient that you have just seen is used by most of the policy-based methods, but the details can vary. One very important point is how exactly gradient scales, Q(s, a), are calculated. In the cross-entropy method from Chapter 4, The Cross-Entropy Method, we played several episodes, calculated the total reward for each of them, and trained on transitions from episodes with a better-than-average reward. This training procedure is a policy gradient method with Q(s, a) = 1 for state and action pairs from good episodes (with a large total reward) and Q(s, a) = 0 for state and action pairs from worse episodes.

The cross-entropy method worked even with those simple assumptions, but the obvious improvement will be to use Q(s, a) for training instead of just 0 and 1. Why should it help? The answer is a more fine-grained separation of episodes. For example, transitions of the episode with the total reward of 10 should contribute to the gradient...