LaTeX中大括號分支公式的書寫

LaTeX中大括號分支公式的書寫：用cases不會換行，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：對齊符號&後面不能出現單個未配對的括號{}