Section: Mathematical Functions
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).  
atan function is defined for all 
arguments x as
 
For real valued variables x, the function is computed directly using 
the standard C library's numerical atan function. For both 
real and complex arguments x, note that generally
 
 due to the periodicity of tan(x).
atan function over the range 
[-1,1].
--> t = linspace(-1,1); --> plot(t,atan(t))
