}\\ \left(\begin{array}{c}\phi_{0}\\\phi_{0} \end{array}\right)_t&=& V\left(\begin{array}{c} \phi_{0}\\\phi_{0} \end{array}\right),\quad V=-\frac{0}{0}\left( \begin{array}{cc} A & B \\ C & -A \\ \end{array} \right), \label{LPT