repeating {HEAD ~ step d} to calculate row values for rows 1 to 2N+1 and storing the row value for each of {TAIL ~ the 2N+1 to 1 rows} in a respective one of memory locations 2N+1 to 1 
repeating { HEAD ~ step d } to calculate row values for rows 1 to 2N+1 and storing the row value for each of { TAIL ~ the 2N+1 to 1 rows } in a respective one of memory locations 2N+1 to 1
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH