Macro for different fonts for math and subscripts

Question

Is it possible to define a macro which (in math mode) typesets normal math and subscripts in different fonts?

Concretely, I am interested in typesetting the math in roman and the subscripts in italic, such that

$\mymacro{A_pB_r}$

would result in

---

In response to an answer, let me clarify that the hope would be that this works on equal footing for a general parameter string (at least as long as it only includes characters and alphanumerical subscripts), such as $A_pB_r$, $ABC_s$, $A_xBC_y$, and so further. Clearly, this can be broken down to individual letters with & without subscripts, but this would make the involved expressions extremely cumbersome and lengthy to type up.

Answer 1

\documentclass{article}

\def\mymacro#1{\mbox{$\textfont1=\textfont0 #1$}}

\begin{document}

$\mymacro{A_pB_r}$

\end{document}

Answer 2

The unicode-math package supports this through the \setmathfont[script-font = ...] option. Here is a contrived example that sets the script font to XITS Math:

\documentclass[varwidth, preview]{standalone}
\usepackage{unicode-math}

\setmathfont[Scale = MatchLowercase,
             script-font = XITS Math
            ]{Latin Modern Math}

\begin{document}
\( t_x + \beta_\rho = b_a
\)
\end{document}

For comparison, using the default settings:

According to §4.2 of the unicode-math manual, this is intended to be used with fonts such as Minion Math. However, some families of text fonts package the smaller size as a different font, for example, to use Aldus as the script size for Palatino.

If your font comes with optical sizes but not mathematical script sizes, you would select those with script-features and sscript-features.

ETA

It’s possible to change the math font in the middle of a document or to have more than one math version. If you want to set only a few subscripts in a particular font, one way to do it is _\text{...}, then use text-mode font-selection commands inside the braces. Optionally wrap that in \mathord{} or \mathop{}, as appropriate. If you do this more than once, make it a comamnd in your preamble.

Answer 3

Maybe that? It's definitely not the best answer, but (at least) a proposal …

\documentclass{article}
\usepackage{amsmath,amssymb,amsfonts}
\newcommand{\mycom}[2]{\mathrm{#1}_{#2}}
\begin{document}
    \Huge
    \[
        \mycom{A}{p} \ \mycom{B}{r}
    \]
\end{document}

Here is the output: