Function: asinh
Section: transcendental
C-Name: gasinh
Prototype: Gp
Help: asinh(x): inverse hyperbolic sine of x.
Doc: principal branch of $\sinh^{-1}(x) = \log(x + \sqrt{1+x^{2}})$. In
 particular $\Im(\text{asinh}(x))\in [-\pi/2,\pi/2]$.
 The branch cut is in two pieces: $]-i \infty ,-i]$, continuous with quadrant
 III and $[+i,+i \infty[$, continuous with quadrant I.

