As we studied in Chapter 3, Artificial Intelligence and Machine Learning, an artificial neural network (ANN) is a connected group of artificial neurons that is aggregated into three types of linked neural layers—the input layer, zero or more hidden layers, and the output layer. A monolayer ANN consists of just one layer of links between the input nodes and output nodes, while multilayer ANNs are characterized by the segmentation of artificial neurons across multiple linked layers.
An ANN where signals are propagated in one direction only—that is, the signals are received by the input layer and forwarded to the next layer for processing—are called feedforward networks. ANNs where a signal may be propagated back to artificial neurons or neural layers that have already processed that signal are called feedback networks.
Backwards propagation...