(PHP 4, PHP 5)
atan2 — Arc tangent of two variables
$y
    , float $x
    )
   This function calculates the arc tangent of the two variables
   x and y.  It is
   similar to calculating the arc tangent of
   y / 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).
yDividend parameter
xDivisor parameter
   The arc tangent of y/x 
   in radians.