# Two lines in an equation of one line

What I want to do is to include two lines at the begging in an one-line equation, just like in the following picture.

Does anyone have any idea in order to achieve it? Thanks a lot.

• \max_{x\in\mathcal{J}(k)}\left\{... – David Carlisle Apr 2 '14 at 13:27
• \max requires amsmath. for a more general discussion of math operators, see newcommand vs. DeclareMathOperator. for a list of operators defined in this way, see the amsmath documentation -- texdoc amsmath on a tex live system. – barbara beeton Apr 2 '14 at 13:32
• Depending on how new you are to LaTeX, note that barbara's comment about amsmath means that you need \usepackage{amsmath} in the preamble of your document. – Steven B. Segletes Apr 2 '14 at 13:34
• @barbarabeeton try latex \\show\\max :-) – David Carlisle Apr 2 '14 at 13:46
• @Werner Ehm, I don't think this question is about the vertical bar, but about the max with subscript. – Torbjørn T. Apr 2 '14 at 17:55

## 2 Answers

Using mathtools (that loads amsmathanyway) and its DeclarePairedDelimiterX command, you can have a better spacing for |, and a better control on the size of the braces:

    \documentclass[12pt,a4paper,leqno]{article}

\usepackage[utf8]{inputenc}
\usepackage{amssymb, mathtools}
\usepackage{textcomp}

\DeclarePairedDelimiterX{\set}[2]{\{}{\}}{#1 \delimsize\vert #2}
\newcommand*\Set[1]{\set*{#1}}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}

\let\emptyset\varnothing

\begin{document}
\begin{align}
\tag*{With \texttt{\textbackslash Big}:}       &  \max_{\mathbf x \in \mathcal J(\mathbf K)}\!{\set[\Big]{\sum_{i\in I}\mathcal G_{i  \abs{C_i}}(\mathbf{\Pi}_i, y_i, \emptyset)}{(\mathbf\Pi, y_i)\in \mathcal N(\mathbf x_i)}} \\
\tag*{With \texttt{\textbackslash bigg}:}       & \max_{\mathbf x \in \mathcal J(\mathbf K)}\!{\set[\bigg]{\sum_{i\in I}\mathcal G_{i  \abs{C_i}}(\mathbf{\Pi}_i, y_i, \emptyset)}{(\mathbf\Pi, y_i)\in \mathcal N(\mathbf x_i)}}\\
\tag*{With an implicit \texttt{\textbackslash left}:}        & \max_{\mathbf x \in \mathcal J(\mathbf K)}\!{\Set{\sum_{i\in I}\mathcal G_{i  \abs{C_i}}(\mathbf{\Pi}_i, y_i, \emptyset)}{(\mathbf\Pi, y_i)\in \mathcal N(\mathbf x_i)}}
\end{align}

\end{document}


Please always post a complete document not just a fragment:

\documentclass[12pt]{article}

\begin{document}

$\max_{x\in\mathcal{J}(k)}\left\{ \sum_a^b something \middle| something\right\}$

\end{document}

• I'd say that the outer fences a excessively large and the \middle| needs spacing around it. My solution to a similar problem tex.stackexchange.com/a/167749/3929 – daleif Apr 2 '14 at 14:04
• @daleif yes, agreed. and something shouldn't be set in math italic, but I decided not to address those here and concentrate on the question about the subscript to max. – David Carlisle Apr 2 '14 at 14:09