function varmap, x
;+
; NAME:
;	VARMAP
;
; PURPOSE:
; 	Calculate the variance map of a three-dimensional data cube
; 
; CATEGORY:
; 	Image processing
; 
; CALLING SEQUENCE:
; 	value = varmap(ARRAY)
; 
; INPUT:
; 	ARRAY: three-dimensional floating-point data array. The third dimension
; 	is the number of frames in the data cube.
; 
; OPTIONAL INPUT PARAMETERS:
; 	None
; 
; KEYWORD PARAMETERS:
; 	None
; 
; OUTPUT:
; 	Two-dimensional array containing r.m.s. image (square root from the variance map)
; 	of the data cube.
; 
; COMMON BLOCKS:
; 	None.
; 
; SIDE EFFECTS:
; 	None.
; 
; RESTRICTIONS:
; 	None.
; 
; PROCEDURE:
; 	The variance is computed as the difference of the mean squared value and the
; square of the mean value. This allows to avoid double scanning of the data cube.
; 
; MODIFICATION HISTORY:
;	V. Grechnev, 1999. Written.
;-

Sz = size(x)

if Sz(0) ne 3 then message, 'Argument must be 3-D array'

return, sqrt(total(temporary(x*x), 3)/Sz(3) - total(x, 3)^2/Sz(3)^2)

	end