Construct signal flow graph and find system function \(\frac{\mathrm{X}(\mathrm{S})}{\mathrm{U}(\mathrm{S})}\) for the system characterised by following equations:
\[
\begin{aligned}
x & =x_{1}+b_{3} u \\
\dot{x}_{1} & =-a_{1} x_{1}+x_{2}+b_{2} u \\
\dot{x}_{2} & =-a_{2} x_{1}+b_{1} u
\end{aligned}
\]