This function returns the arc tangent of the argument.
Special boundary conditions that affect the results are:
The exact value yielded by this function may vary slightly from implementation to implementation due to differences in the underlying precision of the implementations math routines and the specific algorithm selected to evaluate this function.
The result of this method is the arc-tangent of the passed in value. The result is expressed in radians and ranges from -pi/2 to +pi/2.