1. Introduction: In this article, we'll create a simple neural network with the deeplearning4j (dl4j) library – a modern and powerful tool for machine learning. Before we get started, not that this guide doesn't require a profound knowledge of linear algebra, statistics, machine learning theory and lots of other topics necessary for a well-grounded ML engineer. 2. What Is Deep Learning ? Neural networks are computational models that consist of interconnected layers of nodes. Nodes are neuron-like processors of numeric data. They take data from their inputs, apply some weights and functions to these data and send the results to outputs. Such network can be trained with some examples of the source data. Training essentially is saving some numeric state (weights) in the nodes which later affects the computation. Training examples may contain data items with features and certain known classes of these items (for instance, “this set of 16×16 pixels contains a hand-