- Asynchronous Advantage Actor-Critic Agents (A3C) is an on-policy algorithm, as we do not use a replay buffer to sample data from. However, a temporary buffer is used to collect immediate samples, which are used to train once, after which the buffer is emptied.
- The Shannon entropy term is used as a regularizer—the higher the entropy, the better the policy is.
- When too many worker threads are used, the training can slow down and can crash, as memory is limited. If, however, you have access to a large cluster of processors, then using a large number of worker threads/processes helps.
- Softmax is used in the policy network to obtain probabilities of different actions.
- An advantage function is widely used, as it decreases the variance of the policy gradient. Section 3 of the A3C paper (https://arxiv.org/pdf/1602.01783.pdf) has more regarding this.
- This is an exercise...

TensorFlow Reinforcement Learning Quick Start Guide
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TensorFlow Reinforcement Learning Quick Start Guide
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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)
Preface
Up and Running with Reinforcement Learning
Temporal Difference, SARSA, and Q-Learning
Deep Q-Network
Double DQN, Dueling Architectures, and Rainbow
Deep Deterministic Policy Gradient
Asynchronous Methods - A3C and A2C
Trust Region Policy Optimization and Proximal Policy Optimization
Deep RL Applied to Autonomous Driving
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