A = \left(
 \begin{array}{cccc}
 -2 & -1 & 1 & 2 \\
 0 & -1 & -2 & -3 \\
 0 & -1 & 0 & 3 \\
 0 & 1 & -2 & -5 \\
 \end{array}
\right)