LaTeX math mode and mbox mode

Question

According to a doc I found around

An \mbox within math mode does not use the current math font; rather it uses the typeface of the surrounding running text.

In math mode, I would like to write something like a_{\mbox{foo}}. If I use this, the foo will be quite big, too big. If I write a_{foo}, foo will be in italic.

What is the magic trick to have non-italic, small text?

Answer 1

I personally prefer to use the \text{} command provided by the AMS-LaTeX package. To use this, you need to include the statement

\usepackage{amsmath}

somewhere in your document preamble, and then in any mathematical environment,

a_{\text{foo}}

will produce the desired output. Section 6 of the User’s Guide for the amsmath Package mentions that the \mbox{} equivalent is

a_{\mbox{\scriptsize foo}}

A final option is

a_{\mathrm{foo}}

which is what I used before I discovered AMS-LaTeX and the \text{} command.

Answer 2

I usually use the option a_{\rm foo} since this is the shortest form I am aware of. I'm not sure if there are any caveats though. I guess the proper form is using the form a_{\text{foo}} suggested by las3rjock

Answer 3

You can just type a_{\text{foo}}

I did not try, but it should work

EDIT: as las3rjock said, the \text{.} is provided by the AMS-LaTeX package. So you need to add the \usepackage{amsmath}

Answer 4

You can use the similar commands \mathmbox or \mathmakebox provided by the mathtools package.