Section 11,11: ATAN

 ATAN (real-number)

 A function that 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      |
 |      |see note | QATAN    | REAL*16    | REAL*16     |
 +------+---------+----------+------------+-------------+

 NOTE: QATAN is not available in DEC Fortran.