Book Image

Deep Reinforcement Learning with Python - Second Edition

By : Sudharsan Ravichandiran
Book Image

Deep Reinforcement Learning with Python - Second Edition

By: Sudharsan Ravichandiran

Overview of this book

With significant enhancements in the quality and quantity of algorithms in recent years, this second edition of Hands-On Reinforcement Learning with Python has been revamped into an example-rich guide to learning state-of-the-art reinforcement learning (RL) and deep RL algorithms with TensorFlow 2 and the OpenAI Gym toolkit. In addition to exploring RL basics and foundational concepts such as Bellman equation, Markov decision processes, and dynamic programming algorithms, this second edition dives deep into the full spectrum of value-based, policy-based, and actor-critic RL methods. It explores state-of-the-art algorithms such as DQN, TRPO, PPO and ACKTR, DDPG, TD3, and SAC in depth, demystifying the underlying math and demonstrating implementations through simple code examples. The book has several new chapters dedicated to new RL techniques, including distributional RL, imitation learning, inverse RL, and meta RL. You will learn to leverage stable baselines, an improvement of OpenAI’s baseline library, to effortlessly implement popular RL algorithms. The book concludes with an overview of promising approaches such as meta-learning and imagination augmented agents in research. By the end, you will become skilled in effectively employing RL and deep RL in your real-world projects.
Table of Contents (22 chapters)
18
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19
Index

TD prediction

In the TD prediction method, the policy is given as input and we try to estimate the value function using the given policy. TD learning bootstraps like DP, so it does not have to wait till the end of the episode, and like the MC method, it does not require the model dynamics of the environment to compute the value function or the Q function. Now, let's see how the update rule of TD learning is designed, taking the preceding advantages into account.

In the MC method, we estimate the value of a state by taking its return:

However, a single return value cannot approximate the value of a state perfectly. So, we generate N episodes and compute the value of a state as the average return of a state across N episodes:

But with the MC method, we need to wait until the end of the episode to compute the value of a state and when the episode is long, it takes a lot of time. One more problem with the MC method is that we cannot apply it to non-episodic...