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