COMPLEX-VALUED ADAPTIVE SIGNAL PROCESSING - Adaptive Signal Processing: Next Generation Solutions - page 52

Figure 1.12 (a) Magnitude, (b) phase, (c) real and (d) imaginary responses of atanh.

Figure 1.13 (a) Magnitude and (b) phase responses of tanh.

† MLPs that use continuous nonlinear activation functions without any singular
points can achieve universal approximation of any continuous nonlinear map-
ping over a compact set in C

N . Note that these functions are not bounded, as
shown for the sinh function in Figure 1.16, but by bounding the region of interest
using scaling, for example, for range around the unit circle for the sinh function,
they can be used as activation functions and can provide good approximation as
demonstrated in [63].