The cases environment renders multiple lines with an extensible left curly-brace. It can be used for piecewise-defined functions. For this to work, you must have \usepackage{amsmath} in the preamble.

    \begin{center}
        \emph{$m_{ij}$} :=
        \begin{cases}
        \emph{$w_{ij}$}, if  -1$\leq$\emph{$w_{ij}$}$\leq$1\\ 
        -1, if \emph{$w_{ij}$}$<$-1 \\
        1, if \emph{$w_{ij}$}$>$1 \\
        \end{cases}
LaTeX markup... ...results in: ...is used for:
Rank(x) = \begin{cases} n/2 &\mbox{if } n \equiv 0 \\
(3n +1)/2 & \mbox{if } n \equiv 1 \end{cases} \pmod{2}.
function defined piecewise
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