$M^k = \begin{pmatrix} A^k & 0 \\ 0 & B^k \end{pmatrix}$

$M^k = \begin{pmatrix} A^k & 0 \\ 0 & I \end{pmatrix}$

$M^k = \begin{pmatrix} kA & 0 \\ 0 & kB \end{pmatrix}$

$M^k = A^k + B^k$