The output \( y \) is produced via the activation function \( f \)
$$ y = f\left(\sum_{i=1}^n w_ix_i + b_i\right) = f(z), $$This function receives \( x_i \) as inputs. Here the activation \( z=(\sum_{i=1}^n w_ix_i+b_i) \). In an FFNN of such neurons, the inputs \( x_i \) are the outputs of the neurons in the preceding layer. Furthermore, an MLP is fully-connected, which means that each neuron receives a weighted sum of the outputs of all neurons in the previous layer.