How to rotate a big mathematical operator?

Question

I would like to rotate the \bigcupdot operator, provided by the STIX2 Math font, by 180 degrees about its center. I tried the following code.

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{STIXTwoMath-Regular.otf}
\usepackage{graphicx}
\begin{document}
$[\bigcupdot]\ [\mathop{\rotatebox[origin=c]{180}{\bigcupdot}}]$
\end{document}

The result was this:

Why didn't the rotated version typeset? How can I fix it?

I don't know why LuaTeX doesn't throw an error, but the argument of \rotatebox is always text. You need \rotatebox[origin=c]{180}{$\bigcupdot$}. — campa, Mar 21 '23 at 19:39
Thanks. This solved the problem. Strangely, if you replace \bigcupdot by \cupdot in my original code, the rotated version does typeset, without the dollar signs. — Evan Aad, Mar 21 '23 at 19:44
Sorry, can't help you there I don't use Unicode engines unless my life depends on it... ;-) — campa, Mar 21 '23 at 19:46
it is a side effect of unicode-math that \bigcupdot simply expands to ⨃ which works in text given a suitable font. — David Carlisle, Mar 21 '23 at 19:50
@barbarabeeton: STIX2 doesn't have \bigcapdot (unlike MnSymbol and fdsymbol). — Sandy G, Mar 21 '23 at 20:23
@SandyG -- What!!! It's supposed to. I'll check, and then submit a bug report as appropriate. — barbara beeton, Mar 21 '23 at 20:31
@barbarabeeton Also no \bigcapplus, which would also be helpful. (\biguplus is available.) — Evan Aad, Mar 21 '23 at 21:12
@DavidCarlisle Technically \bigcupdot doesn't "expand". latexdef -t lualatex -p unicode-math bigcupdot ⟹ "\bigcupdot: the character ⨃" — user202729, Mar 22 '23 at 11:48

score 3 · Accepted Answer · answered Mar 21 '23 at 19:52

3

\documentclass[a4paper,12pt]{article}
\usepackage{unicode-math}
\setmathfont{STIXTwoMath-Regular.otf}
\usepackage{graphicx}
\begin{document}
$[\bigcupdot]$  [\rotatebox[origin=c]{180}{$\bigcupdot$}]
\end{document}

answered Mar 21 '23 at 19:52

Sebastiano

54,118

egreg · Answer 2 · 2023-03-22T10:21:37.167

The problem is that \rotatebox typesets its argument in text mode and you would get “Missing $” errors with XeLaTeX, but nothing in LuaLaTeX (unless the current text font happens to have the character.

Anyway, using $\bigcupdot$ isn't enough.

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\usepackage{unicode-math}
\usepackage{graphicx}
\setmathfont{STIXTwoMath-Regular.otf}
\makeatletter
\NewDocumentCommand{\bigcapdot}{}{%
  \mathop{\mathpalette\bigcapdot@\relax}\displaylimits
}
\newcommand{\bigcapdot@}[2]{%
  \vcenter{\hbox{\scalebox{1}[-1]{$\m@th#1\bigcupdot$}}}%
}
\makeatother
\begin{document}
$[\bigcupdot][\bigcapdot]$
[
[\bigcupdot][\bigcapdot]
]
\end{document}

Here twocolumn is just to make a smaller picture.

Why just adding $ around \bigcupdot isn't enough? Look at the comparison below.

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\usepackage{unicode-math}
\usepackage{graphicx}
\setmathfont{STIXTwoMath-Regular.otf}
\makeatletter
\NewDocumentCommand{\bigcapdot}{}{%
  \mathop{\mathpalette\bigcapdot@\relax}\displaylimits
}
\newcommand{\bigcapdot@}[2]{%
  \vcenter{\hbox{\scalebox{1}[-1]{$\m@th#1\bigcupdot$}}}%
}
\makeatother
% for comparison
\newcommand{\simplebigcapdot}{\mathop{\rotatebox[origin=c]{180}{$\bigcupdot$}}}
\begin{document}
\subsubsection*{Scaling}
$[\bigcupdot][\bigcapdot]$
$\scriptstyle[\bigcupdot][\bigcapdot]$
$\scriptscriptstyle[\bigcupdot][\bigcapdot]$
[
[\bigcupdot][\bigcapdot]
]
\subsubsection*{Not scaling}
$[\bigcupdot][\simplebigcapdot]$
$\scriptstyle[\bigcupdot][\simplebigcapdot]$
$\scriptscriptstyle[\bigcupdot][\simplebigcapdot]$
[
[\bigcupdot][\simplebigcapdot]
]
\end{document}

If you need other flipped symbols:

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\usepackage{unicode-math}
\usepackage{graphicx}
\setmathfont{STIXTwoMath-Regular.otf}
\makeatletter
\NewDocumentCommand{\bigcapdot}{}{%
  \genericbigopflip{\bigcupdot}%
}
\NewDocumentCommand{\bigcapplus}{}{%
  \genericbigopflip{\biguplus}%
}
\newcommand{\genericbigopflip}[1]{%
  \mathop{\mathpalette\bigcapdot@{#1}}\displaylimits
}
\newcommand{\bigcapdot@}[2]{%
  \vcenter{\hbox{\scalebox{1}[-1]{$\m@th#1#2$}}}%
}
\makeatother
\begin{document}
$[\bigcupdot][\bigcapdot][\biguplus][\bigcapplus]$
$\scriptstyle[\bigcupdot][\bigcapdot][\biguplus][\bigcapplus]$
$\scriptscriptstyle[\bigcupdot][\bigcapdot][\biguplus][\bigcapplus]$
[
[\bigcupdot][\bigcapdot][\biguplus][\bigcapplus]
]
\end{document}

You wrote: " $\bigcupdot$ isn't enough". Why is it not enough? — Evan Aad, Mar 22 '23 at 05:00
Actually you don't get errors with LuaTeX, which is what puzzled me to start with... — campa, Mar 22 '23 at 09:31
@EvanAad I added a comparison between the two approaches. You judge. — egreg, Mar 22 '23 at 09:31
@campa Oh, yes, the bizarre decision of LuaTeX to allow math symbols not in $. LuaTeX tries to get the character from the text font (and doesn't find it, of course). — egreg, Mar 22 '23 at 09:32
@egreg Isn't it unicode-math developers choice to define it by letting it to a character instead of \Umathchardef it? The latter case I believe should give an error when used in text mode. — user202729, Mar 22 '23 at 11:51
Remark, if correct scaling is needed, it's more user-friendly to use \text instead of \mathpalette as in this other answer of egreg: https://tex.stackexchange.com/a/286069/250119 — user202729, Mar 22 '23 at 11:53
@user202729 In (the current version of) LuaTeX, if a \Umathchardef token is found in text mode, all the information is ignored except for the code point and the character with that code point is typeset from the current font.
Sometimes it's easier to use \text, sometimes it isn't. — egreg, Mar 22 '23 at 11:53

How to rotate a big mathematical operator?

2 Answers2