SUFRAC -- take general (fractional) time derivative or integral of	
	    data, plus a phase shift.  Input is TIME DOMAIN data.	

 sufrac power= [optional parameters] <indata >outdata 			

 Optional parameters:							
	power=0		exponent of (-i*omega)	 			
			=0  ==> phase shift only			
			>0  ==> differentiation				
			<0  ==> integration				

	sign=-1			sign in front of i * omega		
	dt=(from header)	time sample interval (in seconds)	
	phasefac=0		phase shift by phase=phasefac*PI	

 Examples:								
  preprocess to correct 3D data for 2.5D migration			
         sufrac < sudata power=.5 sign=1 | ...				
  preprocess to correct susynlv, susynvxz, etc. (2D data) for 2D migration
         sufrac < sudata phasefac=.25 | ...				
 The filter is applied in frequency domain.				
 if dt is not set in header, then dt is mandatory			

 Algorithm:								
		g(t) = Re[INVFTT{ ( (sign) iw)^power FFT(f)}]		
 Caveat:								
 Large amplitude errors will result if the data set has too few points.


 Credits:
	CWP: Chris Liner, Jack K. Cohen, Dave Hale (pfas)
      CWP: Zhenyue Liu and John Stockwell added phase shift option

 Trace header fields accessed: ns, dt, trid
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