Trigonometric inverse tangent, elementwise.
The inverse of tan, so that if y = tan(x) then x = arctan(y).
Parameters:  x : array_like


Returns:  out : ndarray

See also
Notes
arctan is a multivalued function: for each x there are infinitely many numbers z such that tan(z) = x. The convention is to return the angle z whose real part lies in [pi/2, pi/2].
For realvalued input data types, arctan 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 complexvalued input, arctan is a complex analytical function that has branch cuts [1j, infj] and [1j, infj] and is continuous from the left on the former and from the right on the latter.
The inverse tangent is also known as atan or tan^1.
References
[10]  M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 79. http://www.math.sfu.ca/~cbm/aands/ 
[11]  Wikipedia, “Inverse trigonometric function”, http://en.wikipedia.org/wiki/Arctan 
Examples
We expect the arctan of 0 to be 0, and of 1 to be :
>>> np.arctan([0, 1])
array([ 0. , 0.78539816])
>>> np.pi/4
0.78539816339744828
Plot arctan:
>>> import matplotlib.pyplot as plt
>>> x = np.linspace(10, 10)
>>> plt.plot(x, np.arctan(x))
>>> plt.axis('tight')
>>> plt.show()