ATAN2

 ATAN2 (real-number, real-number)

 Class:  Elemental function - Generic

 Returns the arc tangent of the quotient of the two arguments in
 radians.  If both arguments are zero, the result is undefined.  If
 the first argument is positive, the result is positive.  If the
 first argument is negative, the result is negative.  If the first
 argument is zero, the result is zero.  If the second argument is
 zero, the absolute value of the result is pi/2.

 The range of the result is -pi < result <= pi.

 +------+---------+----------+------------+-------------+        
 | Args | Generic | Specific |  Argument  | Result Type |
 +------+---------+----------+------------+-------------+
 |  2   |  ATAN2  | ATAN2    | REAL*4     | REAL*4      |
 |      |         | DATAN2   | REAL*8     | REAL*8      |
 |      |         | QATAN2   | REAL*16    | REAL*16     |
 +------+---------+----------+------------+-------------+