Overview of this book

Reinforcement learning (RL) is a branch of machine learning that has gained popularity in recent times. It allows you to train AI models that learn from their own actions and optimize their behavior. PyTorch has also emerged as the preferred tool for training RL models because of its efficiency and ease of use. With this book, you'll explore the important RL concepts and the implementation of algorithms in PyTorch 1.x. The recipes in the book, along with real-world examples, will help you master various RL techniques, such as dynamic programming, Monte Carlo simulations, temporal difference, and Q-learning. You'll also gain insights into industry-specific applications of these techniques. Later chapters will guide you through solving problems such as the multi-armed bandit problem and the cartpole problem using the multi-armed bandit algorithm and function approximation. You'll also learn how to use Deep Q-Networks to complete Atari games, along with how to effectively implement policy gradients. Finally, you'll discover how RL techniques are applied to Blackjack, Gridworld environments, internet advertising, and the Flappy Bird game. By the end of this book, you'll have developed the skills you need to implement popular RL algorithms and use RL techniques to solve real-world problems.
Preface
Free Chapter
Getting Started with Reinforcement Learning and PyTorch
Markov Decision Processes and Dynamic Programming
Monte Carlo Methods for Making Numerical Estimations
Capstone Project – Playing Flappy Bird with DQN
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Solving multi-armed bandit problems with the softmax exploration

In this recipe, we will solve the multi-armed bandit problem using the softmax exploration, algorithm. We will see how it differs from the epsilon-greedy policy.

As we've seen with epsilon-greedy, when performing exploration we randomly select one of the non-best arms with a probability of ε/|A|. Each non-best arm is treated equivalently regardless of its value in the Q function. Also, the best arm is chosen with a fixed probability regardless of its value. In softmax exploration, an arm is chosen based on a probability from the softmax distribution of the Q function values. The probability is calculated as follows:

Here, the τ parameter is the temperature factor, which specifies the randomness of the exploration. The higher the value of τ, the closer to equal exploration it becomes; the lower...