ATAN (real-number)

  Class:  Elemental function - Generic

  Returns the arc tangent of the argument in radians.

  +------+---------+----------+------------+-------------+
  | Args | Generic | Specific |  Argument  | Result Type |
  +------+---------+----------+------------+-------------+
  |  1   |   ATAN  | ATAN     | REAL*4     | REAL*4      |
  |      |         | DATAN    | REAL*8     | REAL*8      |
  |      |         | QATAN    | REAL*16    | REAL*16     |
  +------+---------+----------+------------+-------------+