Inverse hyperbolic tangent elementwise.
x : array_like
out : ndarray
arctanh is a multivalued function: for each x there are infinitely many numbers z such that tanh(z) = x. The convention is to return the z whose imaginary part lies in [-pi/2, pi/2].
For real-valued input data types, arctanh always returns real output. For each value that cannot be expressed as a real number or infinity, it yields nan and sets the invalid floating point error flag.
For complex-valued input, arctanh is a complex analytical function that has branch cuts [-1, -inf] and [1, inf] and is continuous from above on the former and from below on the latter.
The inverse hyperbolic tangent is also known as atanh or tanh^-1.
|[R14]||M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 86. http://www.math.sfu.ca/~cbm/aands/|
|[R15]||Wikipedia, “Inverse hyperbolic function”, http://en.wikipedia.org/wiki/Arctanh|
>>> np.arctanh([0, -0.5]) array([ 0. , -0.54930614])