atan(RR,RR) -- arctangent function

atan(RR,RR) -- arctangent function

Synopsis:

Usage: t = atan(x,y)

Function: atan -- arctangent function

Input:

x, an instance of class RR.

y, an instance of class RR.

Output:

y, an instance of class RR: the angle formed with the x-axis by the ray from the origin to the point {x,y}