;-----------------------------------------------------------------
; derivate.pro
;
; written by Andreas Reigber
;------------------------------------------------------------------
; Calculates the derivative of a 1D-array
;
; Usage:
; res = derivate(arr)
;------------------------------------------------------------------
; This software has been released under the terms of the GNU Public
; license. See http://www.gnu.org/copyleft/gpl.html for details.
;------------------------------------------------------------------
function derivate,array
   s=size(array)
   if s(0) ne 1 then begin
   	print,"Array not one-dimensional"
   	return,-1
   endif
   anz = s(1)
	back = array - shift(array,1)
	back(0) = interpol(back(1:*),findgen(anz-1)+1,0)
	return,back
end