A math-font-size-knowledgeable \raisebox

Question

I would like to some symbols lower than others in a math formula, without size change, for example

\def\abcd#1#2{\left[\raisebox{-.4em}{{\ensuremath{#1}}}\kern-.3em\setminus\kern-.2em#2\right]}
$\abcd{X_1}{X_2}$

which gives

But when I use this notation in a subscript position $$\bigoplus_{\abcd{X_1}{X_2}}$$, the left glyph remains at normalsize (because of the \raisebox acting like a \hbox and ignoring the fact that it is located in a subscript):

How can I define a math-font-size-knowledgeable \raisebox command?

https://tex.stackexchange.com/questions/5191/ – user94293 May 21 '21 at 04:10 — user94293, May 21 '21 at 04:10

score 3 · Accepted Answer · answered May 21 '21 at 04:30

3

You can use \mathpalette plain TeX macro:

\def\abcd#1#2{\left[\mathpalette\abcdA{#1}\mkern-6mu{\setminus}#2\right]}
\def\abcdA#1#2{\lower.4em\hbox{$#1#2$}}

Moreover, the \setminus is re-typed as Ord using {\setminus}, so you needn't compensate the space after it by negative kern. And the first negative kern is expressed in mu units in order to work in script sizes too.

answered May 21 '21 at 04:30

wipet

74,238

It works, thanks! Boy is the\mathpalette macro weird! – yannis May 21 '21 at 08:59
\backslash has been in plain TeX from day 1. – egreg May 21 '21 at 10:18

score 2 · Answer 2 · answered May 21 '21 at 10:16

You don't have to guess the amount of lowering. It's necessary to use \mathpalette in order to use the right font size. See The mysteries of \mathpalette

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\abcd}[2]{\left[\mathpalette\abcd@{#1}\backslash#2\right]}
\newcommand{\abcd@}[2]{%
  % #1 = math style
  % #2 = text to be lowered
  \raisebox{%
    % we make it so that the top of the
    % lowered part is at the formula axis
    \dimexpr-\height+\abcd@fontdimen{#1}%
  }{%
    % we don't want that \scriptspace kicks in
    \scriptspace=\z@
    % the part to be lowered
    $\m@th#1#2$%
  }%
}
\newcommand{\abcd@fontdimen}[1]{%
  % the height of the formula axis is \fontdimen22 <math font of family 2>
  \fontdimen22
  \ifx#1\displaystyle\textfont\else
  \ifx#1\textstyle\textfont\else
  \ifx#1\scriptstyle\scriptfont\else
  \scriptscriptfont\fi\fi\fi 2
}
\makeatother
\begin{document}
[
\abcd{X_1}{X_2}\qquad\bigoplus_{\abcd{X_1}{X_2}}
]
[
\abcd{X}{Y}\qquad\bigoplus_{\abcd{X}{Y}}
]
\end{document}

A math-font-size-knowledgeable \raisebox

2 Answers2