Giving subset of equations big accolade

I want to give a subset of equations, grouped together, in an eqnarray a big accolade to the right together with a short mathematical expression. What would be the best way to do so?

\begin{eqnarray*}
\sum_{k}x_{i - 11, k} + \dots + \sum_{k}x_{i - 2, k} &\ge& x_{i, 1}, \\
\sum_{k}x_{i - 1, k} &\le& 1 - x_{i, 1}, \\
\sum_{k}x_{i - 1, k} &\le& 1 - x_{i, 1},  \quad \quad   1 < i \le 11.
\end{eqnarray*}


An example of what I mean

If I should use something different to an eqnarray then I will do so.

• You should never use eqnarray to begin with. Dec 22, 2021 at 11:23

Never use eqnarray, see eqnarray vs align

You can use the very powerful nicematrix package instead:

\documentclass{article}
\usepackage{amsmath}
\usepackage{nicematrix}

\begin{document}

$\newcolumntype{R}{>{\displaystyle}r} \newcolumntype{L}{>{\displaystyle}l} \begin{NiceArray}{@{} R<{{}} @{} LL} \smash[t]{\vphantom{\bigg|}} \sum_{k}x_{i - 11, k} + \dots + & \sum_{k}x_{i - 2, k} \ge x_{i, 1}, & \Block{2-1}{i>11} \\ \vphantom{\bigg|} &\sum_{k}x_{i - 1, k} \le 1 - x_{i, 1}, \\ \smash[b]{\vphantom{\bigg|}} &\sum_{k}x_{i - 1, k} \le 1 - x_{i, 1}, & 1 < i \le 11. \CodeAfter\SubMatrix.{1-2}{2-2}\} \end{NiceArray}$

\end{document}


The tricks are:

1. \vphantom{\bigg|} to ensure better spacing between rows; it's top- and bottom-smashed in the first and last;
2. \CodeAfter for the decoration;
3. \Block for the condition to be midway.

You may use the IEEEeqnarraybox environment. See Appendix F of this article for more information about the environment.

\documentclass{article}

\usepackage{amsmath}
\usepackage{IEEEtrantools}

\begin{document}
\begin{IEEEeqnarray*}{rl}
\begin{IEEEeqnarraybox}[\relax][c]{rCl}
\sum_{k}x_{i - 11, k} + \dots + \sum_{k}x_{i - 2, k} & \ge & x_{i, 1}, \\
\sum_{k}x_{i - 1, k} & \le & 1 - x_{i, 1},\quad \quad
\end{IEEEeqnarraybox}
& \Bigg\} i > 11
\\
\begin{IEEEeqnarraybox}{rCl}
\sum_{k}x_{i - 1, k} & \le & 1 - x_{i, 1},\quad \quad
\end{IEEEeqnarraybox}
& 1 < i \le 11.\\
\end{IEEEeqnarray*}
\end{document}


The placement of the curly brace doesn't seem to be exactly in the center.