Book Image

Advanced Deep Learning with TensorFlow 2 and Keras - Second Edition

By : Rowel Atienza
Book Image

Advanced Deep Learning with TensorFlow 2 and Keras - Second Edition

By: Rowel Atienza

Overview of this book

Advanced Deep Learning with TensorFlow 2 and Keras, Second Edition is a completely updated edition of the bestselling guide to the advanced deep learning techniques available today. Revised for TensorFlow 2.x, this edition introduces you to the practical side of deep learning with new chapters on unsupervised learning using mutual information, object detection (SSD), and semantic segmentation (FCN and PSPNet), further allowing you to create your own cutting-edge AI projects. Using Keras as an open-source deep learning library, the book features hands-on projects that show you how to create more effective AI with the most up-to-date techniques. Starting with an overview of multi-layer perceptrons (MLPs), convolutional neural networks (CNNs), and recurrent neural networks (RNNs), the book then introduces more cutting-edge techniques as you explore deep neural network architectures, including ResNet and DenseNet, and how to create autoencoders. You will then learn about GANs, and how they can unlock new levels of AI performance. Next, you’ll discover how a variational autoencoder (VAE) is implemented, and how GANs and VAEs have the generative power to synthesize data that can be extremely convincing to humans. You'll also learn to implement DRL such as Deep Q-Learning and Policy Gradient Methods, which are critical to many modern results in AI.
Table of Contents (16 chapters)
14
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15
Index

5. Advantage Actor-Critic (A2C) method

In the Actor-Critic method from the previous section, the objective is for the value function to evaluate the state value correctly. There are other techniques for training the value network. One obvious method is to use mean square error (MSE) in the value function optimization, similar to the algorithm in Q-learning. The new value gradient is equal to the partial derivative of the MSE between the return, Rt, and the state value:

(Equation 10.5.1)

As , the value network prediction gets more accurate in predicting the return for a given state. We refer to this variation of the Actor-Critic algorithm as Advantage Actor-Critic (A2C). A2C is a single-threaded or synchronous version of the Asynchronous Advantage Actor-Critic (A3C) by [3]. The quantity is called the Advantage.

Algorithm 10.5.1 summarizes the A2C method. There are some differences between A2C and Actor-Critic. Actor-Critic is online or is trained on a per...