Arctangent (inverse tangent) function.

**X**- must be of type real.

**Class**

Elemental function

**Result Type and Attributes**

Same as X.

**Result Value**

- It is expressed in radians and approximates arctan(X).
- It is in the range -&pi./2 <= ATAN(X) <= &pi./2.

**Examples**

ATAN (1.0) approximates &pi./4.

Specific Name | Argument Type | Result Type | Pass As Arg? |
---|---|---|---|

ATAN | default real | default real | yes |

DATAN | double precision real | double precision real | yes |

QATAN (1)
| REAL(16) | REAL(16) | yes |

**Notes: **

- IBM Extension.