The observability matrix for the given signal flow graph is
1
\(\left[ {\begin{array}{*{20}{c}}
1&{ - 2}\\
{ - 2}&4
\end{array}} \right]\)
2
\(\left[ {\begin{array}{*{20}{c}}
1&0\\
0&1
\end{array}} \right]\)
3
\(\left[ {\begin{array}{*{20}{c}}
1&0\\
0&{ - 1}
\end{array}} \right]\)
4
\(\left[ {\begin{array}{*{20}{c}}
1&2\\
2&4
\end{array}} \right]\)