function WDNDYDHI, x,qmf
;+
; NAME:
; 	WDNDYDHI
;
; PURPOSE:
;	This function performs a Hi-Pass Downsampling operation. 
;	(periodized).
;
; CATEGORY:
;	Wavelets
;
; CALLING SEQUENCE:
;    d = WDNDYDHI(x,f)
;
; INPUTS:
;    x:		1-d signal at fine scale.
;    f:		filter
;
; OUTPUTS:
;    y:		1-d signal at coarse scale.
;
; EXAMPLE:
;
; SEE ALSO:
;	wdndydlo, wupdydhi, wupdydlo, wfwtpo, wiconv
;
; MODIFICATION HISTORY:
; 	Written by:	Amara Graps		October, 1994
;Translated from MatLab Wavelab routine: downdyadhi.m
;-

	d = WICONV( WMIRFILT(qmf),WLSHIFT(x))
	n = N_ELEMENTS(d)
	
	;use the IDL way to create an index array
	a = 1	;val of 1st element
	b = 2	;increment
	c = n-1	;val of last element
	indx_array = WMKIARRY( a, b, c)		
	d = d(indx_array)
;
; Algorithm Source:  WaveLab Version 0.600
; WaveLab WWW site: http://playfair.stanford.edu/ 
; WaveLab Questions? e-mail wavelab@playfair.stanford.edu
;   
    

RETURN, d 
End 
;***************************************************