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