Input: $a = [[1 .. 4], [5 .. 8], [9 .. 12]]
Output: $b = [[14, 18, 22], [30, 34, 38]]

Input: $a = [[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]
Output: $b = [[2, 1, 0], [1, 2, 1], [0, 1, 2]]