while($0 < H * W)
 $1 = ($0 / W) + 1
 $2 = ($0 % W) + 1
 $3 = A[$1,$2] - B[$1,$2]
 $4 = $4 + $3
 $5 = $5 + ($3 * $1)
 $6 = $6 + ($3 * $2)
 $0 = $0 + 1
end
return($5 / $4, $6 / $4)