SUCHW - Change Header Word using one or two header word fields	

  suchw <stdin >stdout [optional parameters]				

 Required parameters:							
 none									

 Optional parameters:							
 key1=cdp,...	output key(s) 						
 key2=cdp,...	input key(s) 						
 key3=cdp,...	input key(s)  						
 a=0,...		overall shift(s)				
 b=1,...		scale(s) on first input key(s) 			
 c=0,...		scale on second input key(s) 			
 d=1,...		overall scale(s)				

 The value of header word key1 is computed from the values of		
 key2 and key3 by:							

	val(key1) = (a + b * val(key2) + c * val(key3)) / d		

 Examples:								
 Shift cdp numbers by -1:						
	suchw <data >outdata a=-1					

 Add 1000 to tracr value:						
 	suchw key1=tracr key2=tracr a=1000 <infile >outfile		

 We set the receiver point (gx) field by summing the offset		
 and shot point (sx) fields and then we set the cdp field by		
 averaging the sx and gx fields (we choose to use the actual		
 locations for the cdp fields instead of the conventional		
 1, 2, 3, ... enumeration):						

   suchw <indata key1=gx key2=offset key3=sx b=1 c=1 |			
   suchw key1=cdp key2=gx key3=sx b=1 c=1 d=2 >outdata			

 Do both operations in one call:					

 suchw<indata key1=gx,cdp key2=offset,gx key3=sx,sx b=1,1 c=1,1 d=1,2 >outdata


 Credits:
	SEP: Einar Kjartansson
	CWP: Jack K. Cohen
      CWP: John Stockwell, 7 July 1995, added array of keys feature
      Delphi: Alexander Koek, 6 November 1995, changed calculation so
              headers of different types can be expressed in each other