Code: Select all
\begin{align} \label{diffeq2}
\begin{split}
\frac{\partial A_{1}(z)}{\partial z}= i c A_{D}(z) \, , \vspace{2mm} \\
\frac{\partial A_{D}(z)}{\partial z}= i c A_{1}(z) + i c A_{2}(z) \, , \vspace{2mm} \\
\frac{\partial A_{2}(z)}{\partial z}= i c A_{D}(z) \, .
\end{split}
\end{align}