# How can I typeset those braces?

How can I typeset the following expression?

-
en.wikibooks.org/wiki/LaTeX/… –  henrique Apr 18 '14 at 20:57
@AlexNelson i have :undefined control sequence $\displaymode – researcher Apr 18 '14 at 20:58 Heh, I'm working on Java while answering a TeX question, I mean$\displaystyle\bigl\{O^{(i)}, e^{(i)}\bigr\}^{M}_{i=1}\$ –  Alex Nelson Apr 18 '14 at 21:02
@researcher The best answer should probably also mention Knuth notes that squiggly brackets should have some small spacing, \bigl\{\,..., ...\,\bigr\}. Also, using \bigl\{ and \bigr\} works great...for inline or display stuff. For footnotes, I think you should use \left\{...\right\}. –  Alex Nelson Apr 18 '14 at 21:05
@AlexNelson \displaystyle is useless. –  egreg Apr 18 '14 at 21:16

This code should give you what you want:

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{equation*}
\left\{\mathrm{O}^{\left(i\right)},\mathrm{e}^{\left(i\right)}\right\}_{i=1}^M
\end{equation*}
\end{document}


-
I hope you don't mind, I've completed your code to give an MWE. –  LaRiFaRi Apr 19 '14 at 0:44
My guess is that O and e are bold: \mathbf{O}^{(i)} and \mathbf{e}^{(i)} (no need for \left and \right here). –  Heiko Oberdiek Apr 19 '14 at 2:26

To fully reproduce the screenshot you've posted, you need (as also pointed out in a separate comment by Heiko Oberdiek):

• \left\{ and \right\} for auto-scaled curly braces

• \mathbf{O} and \mathbf{e} to typeset "O" and "e" in math-bold

A full MWE (minimum working example):

\documentclass{article}
\begin{document}
$\left\{ \mathbf{O}^{(i)},\mathbf{e}^{(i)} \right\}_{i=1}^M$
\end{document}

-