One or more two-dimensional slices and an optional integer, k.
The value k determines which diagonals will have the function applied: For k = 0, the function is also applied to the main diagonal For k = 1 (default), only the non-main diagonals below the main diagonal will have the function applied. For k > 1, fewer diagonals below the main diagonal will have the function applied. For k < 0, more diagonals above the main diagonal will have the function applied.