----- header of sync_hi.pro extracted on: Wed Jun  3 10:12:53 2009

----- Documentation for /scisoft/xop2.3/src_idl/sources/sync_hi.pro -----
 NAME:
       SYNC_HI

 PURPOSE:
       Calculates the function Hi(x) used for Synchrotron radiation 
	Hi(x) = x^i * BeselK(x/2,2/3) (for total polarization)


 CATEGORY:
       Mathematics.

 CALLING SEQUENCE:
       Result = sync_hi(x [,i] )

 INPUTS:
       x:      the argument of the function. All calculations are done in doble
               precision.
	i:	the exponent. If this optional argument is not entered, it 
		is set to 2.

 KEYWORD PARAMETERS:
	POLARIZATION: 0 Total 
		      1 Parallel       (l2=1, l3=0, in Sokolov&Ternov notation)
		      2 Perpendicular  (l2=0, l3=1)

 OUTPUTS:
       returns the value  of the sync_hi function

 PROCEDURE:
       Uses the relation ship Hi(x) =  x^i * sync_f(0,x)

 MODIFICATION HISTORY:
       Written by:     M. Sanchez del Rio, srio@esrf.fr, 2002-05-23


