# Aligning the cells in a matrix in an equation

I have been trying to align the "<" and ">" after t_{c} with that of the equal "=" sign in the second matrix (see the codes below). Any ideas on how I can do that? I'm using the following codes:

    \begin{equation}
\begin{aligned}
\sigma(t_{c})=\left\{\begin{matrix}
1\\ [0,1]
\\
0
\end{matrix}\right.\text{if } t_{c} \left\{\begin{matrix}
< \\
=\sfrac{-\alpha N(m_{c},m_{e})}{v_{c}^{d}}.\\
>
\end{matrix}\right.\label{eqn:13}


\documentclass{article}
\usepackage{amsmath}
\usepackage{nicefrac}

\begin{document}
\begin{equation}\label{eqn:13}
\sigma(t_{c}) = \begin{cases}
1       &   \\
[0,1]   &  \text{ if } t_c \\
0       &   \\
\end{cases}%
\begin{cases}
< \\
= \nicefrac{-\alpha N(m_{c},m_{e})}{v_{c}^{d}} .\\
>
\end{cases}
\end{equation}
\end{document} • I was wondering what's the difference between \sfrac and \nicefrac.
– OGC
Mar 1, 2021 at 8:11
• @OGC, you not provide MWE, so I don't know, where \sfrac{...}{...} is defined, however the nicefrac packages (for which I'm aware) define \nicefrac{...}{...} which produce similar fraction as you shown on image. You can replace them with your definition if you more prefer them. Mar 1, 2021 at 8:15
• @Zarko: \sfrac is defined by the xfrac package (l3packages bundle). Mar 1, 2021 at 9:13
• @Bernard, thank you very much for info! Mar 1, 2021 at 9:19