D=\left[
\begin{array}{cccc}
1 & 0 & 0 & 0
\vspace{0.5em}\\
0 & -1 & 0 & 0
\vspace{0.5em}\\
0 & 0 & -1 & 0
\vspace{0.5em}\\
0 & 0 & 0 & 0
\vspace{0.5em}\\
\end{array}
\right]