Example of activation function computation for a single neuron. The value of is computed from Eq. (1). The symbols have the meaning specified in Sect. 3.1. In the example shown, n_ℓ = 3 (number of neurons in layer ℓ), i = 1 (neuron considered in layer ℓ + 1), k = 1, 2, 3 (neuron identifiers for layer ℓ). The value of becomes , which is used to compute the activation function value for neurons j in the successive layer ℓ + 2.