# How to implement this symbol in LaTeX? [duplicate]

I wanted to do the sigma enclosures in the below shown equation correctly. Actually this is also expectation symbol, right? I don't know it's name.

## marked as duplicate by yo', m0nhawk, Mico, Svend Tveskæg, Paul GesslerAug 16 '14 at 14:26

• You mean \langle, \rangle? – percusse Aug 16 '14 at 13:43
• @percusse: Yes. Please put it in answer – dexterdev Aug 16 '14 at 13:44

A mathtools solution:

\documentclass{article}

\usepackage{mathtools}

\DeclarePairedDelimiter\ExpValue{\langle}{\rangle}
\newcommand*\diff{\mathop{}\!\mathit{d}}

\begin{document}

$$\ExpValue*{\sigma_{N}^{2}} = \int_{-\infty}^{\infty} \diff\sigma P(\sigma)\sigma^{2} \simeq \delta_{k}\sum_{i = 1}^{k} P(\sigma_{k})\sigma_{k}^{2}$$

\end{document}


Note that with the starred version of \ExpValue, ther delimiters will scale automatically.

P.S. Are you sure that \simeq shouldn't be \approx? (I'm not sure...)

Reproduced equation:

\documentclass[varwidth]{standalone}

\begin{document}
$\langle\sigma_{N}^{2}\rangle = \int_{-\infty}^{\infty}\mathrm{d}\sigma P(\sigma)\sigma^{2} \simeq \delta_{k}\sum_{i=1}^{k} P(\sigma_{k})\sigma_{k}^{2}$
\end{document}


If you are typing lot of physics, then you may consider using physics package. It provides lot of goodies including \expval

\documentclass{article}

\usepackage{physics}

\begin{document}
$\expval{\sigma_{N}^{2}} = \int_{-\infty}^{\infty}\mathrm{d}\sigma P(\sigma)\sigma^{2} \simeq \delta_{k}\sum_{i=1}^{k} P(\sigma_{k})\sigma_{k}^{2}$
$\expval{A}{\Psi} \quad \ev{A}{\Psi} \quad$
\end{document}