# Math-mode kerning/spacing of letters

Take the following two equations:

$$o^{AR}_{i,t} = w^{AR}_i x_t + o^{AR}_{i+1,t-1}$$

$$o^{MA}_{i,t} = w^{MA}_i x_t + o^{MA}_{i+1,t-1}$$

The 'AR' and 'MA' are actually acronyms and are meant to be placed together with no gaps between them. I am aware that Math Mode treats each letter as an individual and doesn't kern them properly. This is particularly evident in the fact that the space between the 'M' and the 'A' is larger than between the 'A' and the 'R'.

Is there any way to get Math Mode to join the letters up more neatly?

• You could use \text{MA}, or \mathrm{MA}. For the difference between them see Is there a preference of when to use \text and \mathrm?. – Peter Grill May 21 '13 at 4:02
• Thanks, although I think that \DeclareMathOperator from that link will be more useful in the long run. – thornate May 21 '13 at 4:19
• I don't think using \DeclareMathOperator in this case makes sense as they are not operators and don't act on other variables. A better solution might be to define a macro for them: \newcommand*{\MA}{\mathrm{MA}} for example. – Peter Grill May 21 '13 at 4:26

As per the comments, I would suggest using \text{MA} or \mathrm{MA} and perhaps defining a macro for them if they are used often:

## Notes:

• In this specific case it does not make sense to use \DeclareMathOperator as per the question these are acronyms and not operators.

## Code:

\documentclass{article}
\usepackage{amsmath}

\newcommand*{\AR}{\text{AR}}%
\newcommand*{\MA}{\mathrm{MA}}%

\begin{document}
$$o^{\AR}_{i,t} = w^{\AR}_i x_t + o^{\AR}_{i+1,t-1}$$

$$o^{\MA}_{i,t} = w^{\MA}_i x_t + o^{\MA}_{i+1,t-1}$$
\end{document}
• In these cases I recommend using \mathrm (if there are only plain ASCII letters) or \textnormal. Consider, though, that these could give different results in a \boldmath context. What's wrong in \text is that the acronym would be typeset in italics if \AR appears in the statement of a theorem, for example. – egreg May 21 '13 at 9:19