Inverse hyperbolic sine elementwise.
Parameters:  x : array_like


Returns:  out : ndarray

Notes
arcsinh is a multivalued function: for each x there are infinitely many numbers z such that sinh(z) = x. The convention is to return the z whose imaginary part lies in [pi/2, pi/2].
For realvalued input data types, arcsinh always returns real output. For each value that cannot be expressed as a real number or infinity, it returns nan and sets the invalid floating point error flag.
For complexvalued input, arccos is a complex analytical function that has branch cuts [1j, infj] and [1j, infj] and is continuous from the right on the former and from the left on the latter.
The inverse hyperbolic sine is also known as asinh or sinh^1.
References
[8]  M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 86. http://www.math.sfu.ca/~cbm/aands/ 
[9]  Wikipedia, “Inverse hyperbolic function”, http://en.wikipedia.org/wiki/Arcsinh 
Examples
>>> np.arcsinh(np.array([np.e, 10.0]))
array([ 1.72538256, 2.99822295])