atan(RR,RR) -- compute an angle of a certain triangle

Synopsis

Usage:
atan(x,y)
Function: atan
Inputs:
- x, a real number
- y, a real number
Outputs:
- a real number, the angle (in radians) formed with the x-axis by the ray from the origin to the point (x,y)

i1 : atan(sqrt(3.0)/2,1/2)

o1 = 0.523599

o1 : RR

i2 : -- Notice this is not quite pi/6, but it is within a reasonable epsilon.
     epsilon = 10.^-15;

i3 : abs(atan(sqrt(3.0)/2,1.0/2) - pi/6) < epsilon

o3 = true