Deep learning is an art. But it has some boundaries. Learning the boundaries is essential to develop working solutions and, ultimately, push them for novel creations.

For example, cooking is an art with some boundaries. For instance, most cooks adhere to: salt stays out of desserts. But chefs almost always add salt to desserts because they know the edge of this boundary. They understand that while salt is perceived as a condiment it truly is a flavor enhancer; when added to a dessert it enhances the flavor of every ingredient.

Some chefs push the boundaries further. Claudia Fleming, a distinguished chef from New York, went to an extreme in her pineapple dessert. Each component in it is heavily salted. Yet the dessert is not salty. Instead, each flavor feels magnified. The salt makes the dessert an extraordinary dish.

The point is that an understanding of the constructs of food allows one to create extraordinary recipes. Similarly, an understanding of deep learning constructs enables one to create extraordinary solutions.

This book aims at providing such a level of understanding to a reader on the primary constructs of deep learning: multi-layer perceptrons, long- and short-term memory networks from the recurrent neural network family, convolutional neural networks, and autoencoders.

Further, to retain an understanding, it is essential to develop a mastery of (intuitive) visualizations. For example, Viswanathan Anand, a chess grandmaster, and a five-time world chess champion is quoted in Mind Master: Winning Lessons from a Champion's Life, "chess players visualize the future and the path to winning." There, he alludes that a player is just as good as (s)he can visualize.

Likewise, the ability to intuitively visualize a deep learning model is essential. It helps to see the flow of information in a network, and its transformations along the way. A visual understanding makes it easier to build the most appropriate solution.

This book provides ample visual illustrations to develop this skill. For example, an LSTM cell, one of the most complex constructs in deep learning is visually unfolded to vividly understand the information flow within it in the chapter on long- and short-term memory networks.

The understanding and visualizations of deep learning constructs are shrouded by their (mostly) abstruse theories. The book focuses on simplifying them and explain to a reader how and why a construct works. While the "how it works" makes a reader learn a concept, the "why it works" helps the reader unravel the concept. For example, the chapter on multi-layer perceptrons explains how dropout works followed by why it works?

The teachings in the book are solidified with implementations. This book solves a rare event prediction problem to exemplify the deep learning constructs in every chapter. The book explains the problem formulation, data preparation, and modeling to enable a reader to apply the concepts to other problems.

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This book is appropriate for graduate and Ph.D. students, as well as researchers and practitioners.

To the practitioners, the book provides complete illustrative implementations to use in developing solutions. For researchers, the book has several research directions and implementations of new ideas, e.g., custom activations, regularizations, and multiple pooling.

In graduate programs, this book is suitable for a one-semester introductory course in deep learning. The first three chapters introduce the field, a working example, and sets up a student with TensorFlow. The rest of the chapters present the deep learning constructs and the concepts therein.

These chapters contain exercises. Most of them illustrate concepts in the respective chapter. Their practice is encouraged to develop a stronger understanding of the subject. Besides, a few advanced exercises are marked as optional. These exercises could lead a reader to develop novel ideas.

Additionally, the book illustrates how to implement deep learning networks with TensorFlow in Python. The illustrations are kept verbose and, mostly, verbatim for readers to be able to use them directly. The link to the code repository is also available at GitHub.

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My journey in writing this book reminded me of a quote by Dr. Frederick Sanger, a two-time Nobel laureate, "it is like a voyage of discovery, seeking not for new territory but new knowledge. It should appeal to those with a good sense of adventure."

I hope every reader enjoys this voyage in deep learning and find their adventure.

-Chitta Ranjan