5.1 ( ) Consider a two-layer network function of the form (5.7) in which the hiddenunit nonlinear activation functions g(·) are given by logistic sigmoid functions of the form

σ

(a) = {1 + exp(−a)}−1 . (5.191)

Show that there exists an equivalent network, which computes exactly the same function, but with hidden unit activation functions given by tanh

(a) where the tanh function is defined by (5.59). Hint: first find the relation between σ

(a) and tanh(a), and then show that the parameters of the two networks differ by linear transformations.