The ATAN function returns a numeric value in radians
that approximates the arctangent of the argument specified.
The function type is numeric.

Format
>>-FUNCTION ATAN--(--argument-1--)-----------------------------><
- argument-1
- Must be class numeric.
The returned value is the approximation of the arctangent of argument-1 and is greater than -Pi/2 and less than +Pi/2.