# Force placement of sum operands over index

I want to force the operands of a sum to be placed above an "extended" (longer than usual) index, instead of increasing the width of the sum (in the example, see the sums in (2), which are much wider than in (1), because of the different index). I need this for space reasons, the formula is bigger than in the MWE. Do you have any ideas how to achieve this? \documentclass[12pt]{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\text{\textbf{Total Cost }}
&= \sum_{m=1}^{55} 10,000 \cdot Z_m + 7,000 \cdot K_m \\
&= \sum_{i \in \{m | Z_m = 1\}} 10,000 + \sum_{j \in \{k | K_m = 1\}}
7,000
\end{align}

\end{document}

• Did you try \mathclap from mathtools? – nidhin Nov 17 '18 at 19:59

## 3 Answers

Use mathclap from mathtools package.

\documentclass[12pt]{article}
%\usepackage{amsmath}
\usepackage{mathtools}

\begin{document}
\begin{align}
\text{\textbf{Total Cost }}
&= \sum_{m=1}^{55} 10,000 \cdot Z_m + 7,000 \cdot K_m \\
&= \sum_{\mathclap{i \in \{m | Z_m = 1\}}} 10,000 + \sum_{\mathclap{j \in \{k | K_m = 1\}} }
7,000
\end{align}
\end{document} mathtools loads amsmath. \documentclass[12pt]{article}
\usepackage{mathtools}

\begin{document}

\begin{align}
\textbf{Total Cost} % no trailing space inside braces
&= \sum_{m=1}^{55} 10,000 \cdot Z_m + 7,000 \cdot K_m \\
&= \sum_{\mathclap{i \in \{m\, | \, Z_m = 1\}}} 10,000 + \sum_{\mathclap{j \in \{k\, | \, K_m = 1\}}} 7,000
\end{align}

\end{document}

• few seconds .. :) – nidhin Nov 17 '18 at 20:03
• Hi Sigur, I accepted @nidhin's answer, since he commented 3 minutes before posting his own answer and thus was a little faster. Thanks very much though for the quick and helpful answer, I appreciate the effort! – ncw Nov 17 '18 at 20:12
• @ncw, no problem. Just pay attention in my comments on trailing spaces. Also, only \textbf is enough. – Sigur Nov 17 '18 at 20:15

A variant, with the \smashoperator command from mathtools – and some improvements with siunitx, so the comma separator in numbers doesn't add a space.

\smashoperator can take an optional argument, [l] or [r] which are equivalent to \mathlap or \mathrlap respectively. I demonstrate it in a $3$rd equation:

\documentclass[12pt]{article}
\usepackage{mathtools}
\usepackage{siunitx}

\begin{document}

\sisetup{group-digits = integer, group-separator={,}, group-minimum-digits = 4}
\begin{align}
\textbf{Total Cost} % no trailing space inside braces
&= \sum_{m=1}^{55} \num{10000} \cdot Z_m + \num{7000} \cdot K_m \\
&= \smashoperator{\sum_{i \in \{m\mid Z_m = 1\}}}\num{10000} + \smashoperator{\sum_{j \in \{k\mid K_m = 1\}}} \num{7000} \\
&= \smashoperator[r]{\sum_{i \in \{m\mid Z_m = 1\}}} \num{10000} + \smashoperator[l]{\sum_{j \in \{k\mid K_m = 1\}}} \num{7000}
\end{align}

\end{document} 