\[
\[
M =
\left| {\begin{array}{cccc}
 1 & 0 & 0 & 0  \\
 0 & 1 & 0 & 0 \\
 0 & 0 & 1 & 0 \\
 0 & 0 & 0 & 1 \\
 \end{array} } \right|
\]