1.
\begin{eqnarray} Ly = \lambda y \end{eqnarray}
2.
\begin{gather*} \begin{split} b=1\\ a=b \end{split}\\[6pt] \end{gather*}
3.
\begin{gather*} \begin{split} a &= m\ &= k \end{split}\\[6pt] \begin{align} b &= i ,\c &= j \end{align} \end{gather*}
原文：http://www.cnblogs.com/huangshiyu13/p/6919664.html