ATAN2D (real-number, real-number)

  Class:  Elemental function - Generic

  Returns the arc tangent of the quotient of the two arguments in
  degrees.

  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 90 degrees.  The value of
  the argument must be greater than zero.

  The range of the result is -180 degrees < result <= 180 degrees.

  +------+---------+----------+------------+-------------+
  | Args | Generic | Specific |  Argument  | Result Type |
  +------+---------+----------+------------+-------------+
  |   2  | ATAN2D  | ATAN2D   | REAL*4     | REAL*4      |
  |      |         | DATAN2D  | REAL*8     | REAL*8      |
  |      |         | QATAN2D  | REAL*16    | REAL*16     |
  +------+---------+----------+------------+-------------+