Introducing deep learning

While a more detailed discussion of learning algorithms will be addressed in Chapter 4, Learning from Data, in this section, we will deal with the fundamental concept of a neural network and the developments that led to deep learning.

The model of a neuron

The human brain has input connections from other neurons (synapses) that receive stimuli in the form of electric charges, and then has a nucleus that depends on how the input stimulates the neuron that can trigger the neuron's activation. At the end of the neuron, the output signal is propagated to other neurons through dendrites, thus forming a network of neurons.

The analogy of the human neuron is depicted in Figure 1.3, where the input is represented with the vector x, the activation of the neuron is given by some function z(.), and the output is y. The parameters of the neuron are w and b:

Figure 1.3 - The basic model of a neuron

The trainable parameters of a neuron are w and b, and they are unknown...