The
haversine function Haversine[z] is defined by
sin2 (z/2). The
inverse haversine function InverseHaversine[z] is defined by

. The
Gudermannian function Gudermannian[z] is defined as

. The
inverse Gudermannian function InverseGudermannian[z] is defined by
gd-1 (z)=log[tan (z/2+
/4)]. The Gudermannian satisfies such relations as
sinh (z)=tan[gd (x)]. The sinc function
Sinc[z] is the Fourier transform of a square signal.
There are a number of additional trigonometric and hyperbolic functions that are sometimes used. The
versine function is sometimes encountered in the literature and simply is
vers (z)=2hav (z). The
coversine function is defined as
covers (z)=1-sin (z). The complex exponential
eix is sometimes written as
cis (x).