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what is the correct way of typesetting words in indices for example \varphi_{el} looks weird because it is in italics. Is this right? \varphi_\text{el} same for \oint_{Volume} and \oint_\text{Volume}.

And since I think the _\text{} version looks better does this affect normal indices as well; so \sum_i F_i of \sum_\text{i} F_\text{i}

Is there a standard, because I have seen both out in the wild. Or is there an easier way of typesetting this?

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  • 2
    It's not because words are typeset in italic, but because their inter-letter spacing is larger than the normal spacing inside words. And no, an index is a variable, and should be typed in math italic (at least for lowercase, since this depends on the convention for each language: in French, capital letters are – should be– typeset in roman). – Bernard Jul 5 '17 at 8:54
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The general rules are:

  1. Math objects should be typeset in math mode.
  2. As the font carry meaning in math, it is important that a variable is always typeset in the same way. It should not be in one equation in bold and in the next in italic.

This means that \text is normally not the correct command for multiletter variables. As the name indicates it switches to text mode; also it follows the surrounding font. Use it only as a workaround if your variable names contains chars like umlauts or accented chars that doesn't work with \mathXX.

In all other cases use the \mathXX commands, which one depends on the conventions of your field.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}

\begin{document}

$\varphi_{\mathrm{el}} = 1 \text{ and } \varphi_{\text{\normalfont äl}} = 2 $  

$\varphi_{\mathit{el}} = 1 \text{ and } \varphi_{\text{\normalfont\itshape äl}} = 2 $  


\bfseries 
$\varphi_{\mathrm{el}} = 1 \text{ and } \varphi_{\text{\normalfont äl}} = 2 $

$\varphi_{\mathit{el}} = 1 \text{ and } \varphi_{\text{\normalfont\itshape äl}} = 2 $

\end{document}

enter image description here

  • Thanks! Is there a list of those conventions somewhere? – Hans Jul 5 '17 at 9:28
  • Just as a help to future people: in Germany everything inside an equation has to be in italics (DIN 1338). So I am using _\mathit from hereon. thanks! – Hans Jul 9 '17 at 9:27

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