----- file created by makedoc on: Tue Feb 11 14:15:23 2003
----- Documentation for /scisoft/IDL/scisoft/xaid/src//fastbftr.pro -----

 NAME:
	FASTBFTR

 PURPOSE:
	This procedure calculates the Back Fast Fourier Transform of a set

 CATEGORY:
	XAID xafs data analysis package. 

 CALLING SEQUENCE:

	FASTBFTR, fourier, backftr

 INPUTS:
       fourier:  a 4 col set with r,modulus,real and imaginary part
               of a Fourier Transform of an Exafs spectum, as produced
               by FTR or FASTFTR procedures
       backftr: a 4-column set with the  conjugated variable k (col 0),
       the real part (col 1), the modulus (col 2) and phase (col 3)
       of the Back Fourier Transform

 OPTIONAL INPUTS:
	
 KEYWORD PARAMETERS:
	KRANGE=[kmin,kmax] : range of the conjugated variable for 
		the transformation (default = [2,15])
	NPOINT= number of points of the the fft calculation (default = 4096)
	RSTEP = when this keyword is set then the fourier set is 
		interpolated using the indicated value as step. Otherwise
		the fourier set is not interpolated.
	GROUP = the widget group leader Id. Used together with the 
		Dialog_Parent keyword in Dialog_Message(s).

 OUTPUTS:
       This procedure returns a 4-columns array (backftr) with
       the conjugated variable (k) in column 0, the real part of the
       BFT in col 1, the modulus in col 2 and the phase in col 3.

 OPTIONAL OUTPUTS:

 COMMON BLOCKS:

 SIDE EFFECTS:
	None

 RESTRICTIONS:
	None

 PROCEDURE:
	Uses the IDL's FFT function

 EXAMPLE:
               FASTBFTR,fourier,backftr,krange=[2,12]

 MODIFICATION HISTORY:
 	Written by:	Manuel Sanchez del Rio. ESRF
	March, 1993	
	98-10-26 srio@esrf.fr uses Dialog_Message for error messages.

