\begin{align}
\mathcal{G}_n&=\exp[\mathbf{i}\frac{\alpha-\alpha_n}2(m-n)]\\
\mathcal{G}_s&=\exp[-\mathbf{i}(\alpha-\alpha_s)(m-n)]
\end{align}
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
a=b
\end{equation}
\begin{subequations}
\renewcommand{\theequation}{\theparentequation--\arabic{equation}}
\begin{align}
c=d\\
e=f
\end{align}
\end{subequations}
\end{document}
谢谢解答