4

enter image description here

I'm looking for this double-X symbol. Is this available in some package? If not, would it somehow be possible to recreate this symbol by creating a new symbol which consists of two Xs printed on top of each other?

  • Are you aware of this post? – user121799 Dec 7 '17 at 16:24
  • Thank you, detexify did not find anything unfortunately.. – Epiousios Dec 7 '17 at 16:29
  • welcome to tex.sx. this reminds me of the "smash product" (unicode U+2A33, \smashtimes in unicode-math), but i think it isn't meant to be that. and i don't remember seeing it in any of the "usual" symbol fonts. can you provide more context -- source, meaning, ... -- if it's a "recognized" symbol, it can be requested from unicode if proper documentation is provded. (it's easy enough to construct, but i'd prefer some clarification first.) – barbara beeton Dec 7 '17 at 16:46
  • @barbarabeeton It's an abbreviation for the vector (X_1,...,X_n) and it's introduced on page 14 of this book: books.google.de/… – Epiousios Dec 7 '17 at 16:51
  • 2
    Note that perhaps that is intended as a boldface X, but was typed in such way because of a lack of a better option. – Pedro Tamaroff Dec 7 '17 at 23:03
8

You should define a macro for that symbol, say \XX that inserts a negative space between the two X's. This space should depend on where it's used inside math mode (using \mathchoice):

enter image description here

\documentclass{article}

\usepackage{amsmath}

\newcommand{\XX}{% Space between XX varies depending on where it's used
  \mathchoice% https://tex.stackexchange.com/q/148740/5764
    {X\mskip-12.5mu X}% \displaystyle
    {X\mskip-12.5mu X}% \textstyle
    {X\mskip-12mu X}% \scriptstyle
    {X\mskip-11.5mu X}% \scriptscriptstyle
}

\begin{document}

\[
  \text{Var} \bigl( \hat{\beta} \,\vert\, \XX \bigr) \quad \XX^{\XX^{\XX}}
\]

\end{document}
  • Funny. Just after I commented, that one should use math choices your answer pops up :) – Skillmon likes topanswers.xyz Dec 7 '17 at 16:34
  • You should add an additional grouping around the definition of \XX for super- and subscripts. – Skillmon likes topanswers.xyz Dec 7 '17 at 16:46
5

The correct spacing here is to be inserted with \mspace, so it automatically works also in subscripts and superscripts.

\documentclass{article}
\usepackage{amsmath}

\DeclareMathOperator{\Var}{Var}

\newcommand{\doubleX}{{%
  X%
  \mathchoice{\mspace{-12.5mu}}{\mspace{-12.5mu}}{\mspace{-12mu}}{\mspace{-11mu}}%
  X%
}}

\begin{document}

\[
\Var(\hat{\beta} \mid \doubleX)
\,
\doubleX^{\doubleX^\doubleX}_{\doubleX}
\]

\end{document}

Different choices have to be made for the different styles; the values may change if you use a different font.

enter image description here

  • Why \mspace instead of \mkern? – Andrew Swann Dec 7 '17 at 17:05
  • @AndrewSwann Because it has a more LaTeX-like syntax. – egreg Dec 7 '17 at 17:07
  • In this case the mu is not needed (not bad, but not the key part) because of \mathchoice, right? – Manuel Dec 7 '17 at 17:08
  • @Manuel The mu is certainly needed. – egreg Dec 7 '17 at 17:09
  • @egreg Oh, yes, I mixed concepts. – Manuel Dec 7 '17 at 17:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.