FUNCTION sign, x, NO_PAR_CHECK = no_par_check

; Description: For an input parameter "x", the function determines whether the parameter is 
;              positive, negative or zero, returning a value of "1", "-1" or "0" respectively. 
;              The input parameter "x" may be a scalar, vector or array.
;
; Input Parameters:
;
;   x - INTEGER/LONG/FLOAT/DOUBLE SCALAR/VECTOR/ARRAY - The value of the independent variable.
;
; Return Value:
;
;   The return value is a SCALAR/VECTOR/ARRAY (the same as the input parameter) of INTEGER
;   type that takes a value of "1" where the input parameter is positive, "-1" where the
;   input parameter is negative, and "0" where the input parameter is zero. If the input
;   parameter is not of the correct number type, then the function will return a value of "-2".
;
; Keywords:
;
;   If the keyword NO_PAR_CHECK is set (as "/NO_PAR_CHECK"), then the program will not perform
;   parameter checking on the input parameter, reducing program overheads.
;
; Author: Dan Bramich (dan.bramich@hotmail.co.uk)
;
; History:
;
;   20/04/2009 - Module created (dmb)

;Perform parameter checking if not instructed otherwise

;Set positive elements of the input parameter to "1", and negative elements of the input
;parameter to "-1"

;Return the sign of the input parameter