(PHP 4, PHP 5)
atan2 — Arc tangent of two variables
This function calculates the arc tangent of the two variables
y. It is similar to calculating the arc tangent of
x, except that the signs of both arguments are used to determine the quadrant of the result.
The function returns the result in radians, which is between -PI and PI (inclusive).
The arc tangent of
x in radians.