ATAN ATAN Inverse Trigonometric Arctangent Function

Usage

Computes the atan function for its argument.  The general
syntax for its use is

  y = atan(x)

where x is an n-dimensional array of numerical type.
Integer types are promoted to the double type prior to
calculation of the atan function.  Output y is of the
same size and type as the input x, (unless x is an
integer, in which case y is a double type).  
