arctanh(x, out=None, where=None, **kwargs)¶
Inverse hyperbolic tangent element-wise.
- x : array_like
- Input tensor.
- out : Tensor, None, or tuple of Tensor and None, optional
- A location into which the result is stored. If provided, it must have a shape that the inputs broadcast to. If not provided or None, a freshly-allocated tensor is returned. A tuple (possible only as a keyword argument) must have length equal to the number of outputs.
- where : array_like, optional
- Values of True indicate to calculate the ufunc at that position, values of False indicate to leave the value in the output alone.
- out : Tensor
- Array of the same shape as x.
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
nanand 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
 M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 86. http://www.math.sfu.ca/~cbm/aands/  Wikipedia, “Inverse hyperbolic function”, http://en.wikipedia.org/wiki/Arctanh
>>> import mars.tensor as mt
>>> mt.arctanh([0, -0.5]).execute() array([ 0. , -0.54930614])