LaTeX中大括号分支公式的书写:用cases不会换行,用array可以
\begin{equation} \label{eq:alpha} \hat{F}_{h}^{i}(x,y) =\left\{ \begin{array}{lcl} \quad 0,\quad &if \quad |F_{h}^{i}(x,y)| < \sigma_{L} \\ F_{h}^{i}(x,y),\quad &othersize \end{array},(1 \leq i\leq 3L) \right. \end{equation}注意:对齐符号&后面不能出现单个未配对的括号{}