6.2 BASIC CONCEPTS OF NEURAL NETWORKS: HIDDEN LAYERS
• Complex practical applications require one or more hidden layers between the input and output neurons and a correspondingly large number of weights.
• Many commercial ANN include three and sometimes up to five layers, with each containing 10 to 1,000 processing elements.
• Some experimental ANN use millions of processing elements.
• Because each layer increases the training effort exponentially and also increases the computation required, the use of more then three hidden layers is rare in most commercial system.