New symbol derived from [a, b]

Question

I would like to draw the following new symbol, so that I can use it in sentences.

Which tool would you advise? TikZ?

Thanks

Yes, I just need symbols such as $P$, $Q$, $z$, $a$. Thanks. — Colas, Nov 12 '20 at 12:46
I want to use this symbol in math mode, such as in $[a,b] = { ta + (1-t)b ; t\in [0,1] }$. — Colas, Nov 12 '20 at 12:50
Is there a name for this symbol or a reference to where is used? — Peter Grill, Nov 12 '20 at 19:26
But this usually denotes the interval of integers between $a$ and $b$... — Colas, Nov 13 '20 at 19:03
@MichaelHoppe: Was your professor's use also for integer intervals? Do you know of a reference where this symbol is used? — Peter Grill, Nov 24 '20 at 09:10
@PeterGrill Definitly not for integer intevals -- I've met that notation in lecture of differential geometry ... He introduced it to describe the line segment between two points of a vector space. Unfortunately I can't give a reference. — Michael Hoppe, Nov 24 '20 at 09:59

campa · Accepted Answer · 2024-02-14T14:22:41.450

Before someone comes with a TikZ solution :-)...

\documentclass{article}
% \usepackage{amsmath}
\makeatletter
\newcommand{\foo}[1]{{\mathpalette\foo@{#1}}}
\newcommand{\foo@}[2]{%
   @tempdima=.5\fontdimen5
       \ifx#1\displaystyle\textfont\else
       \ifx#1\textstyle\textfont\else
       \ifx#1\scriptstyle\scriptfont\else
       \scriptscriptfont\fi\fi\fi\tw@
   @tempdimb=\fontdimen8
       \ifx#1\displaystyle\textfont\else
       \ifx#1\textstyle\textfont\else
       \ifx#1\scriptstyle\scriptfont\else
       \scriptscriptfont\fi\fi\fi\thr@@
   \setbox\z@=\vtop{\hbox{$\m@th#1#2$}\kern@tempdima}%
   \setbox\tw@=\vbox{\hrule@width@tempdima@height@tempdimb\kern\ht\z@\kern@tempdima}%
   \vtop{\hbox{\vrule@width@tempdimb\copy\tw@\copy\z@\copy\tw@\vrule@width@tempdimb}\hrule@height@tempdimb}%
}
\makeatother
\begin{document}
$\foo{a,b}$
$\scriptstyle\foo{a,b}$
$\scriptscriptstyle\foo{a,b}$
\medskip
$\displaystyle\foo{-\frac{a}{2},\frac{a}{2}}$
$\foo{-\frac{a}{2},\frac{a}{2}}$
$\scriptstyle\foo{-\frac{a}{2},\frac{a}{2}}$
$\scriptscriptstyle\foo{-\frac{a}{2},\frac{a}{2}}$
\end{document}

The two lengths scale according to the current math style: \@tempdimb is the fraction rule thickness, while \@tempdima is half ex (the latter could be fixed without resorting to \fontdimen).

If you uncomment amsmath then the result will differ slightly in \scriptscriptstyle, where you get

without amsmath:

with amsmath:

With the shorter code

\newcommand*{\foo@}[2]{%
   \@tempdima=.5\fontdimen5
       \ifx#1\displaystyle\textfont\else
       \ifx#1\textstyle\textfont\else
       \ifx#1\scriptstyle\scriptfont\else
       \scriptscriptfont\fi\fi\fi\tw@
   \setbox\z@=\vtop{\hbox{$\m@th#1#2$}\kern\@tempdima}%
   \setbox\tw@=\vbox{\hrule\@width\@tempdima\kern\ht\z@\kern\@tempdima}%
   \vtop{\hbox{\vrule\copy\tw@\copy\z@\copy\tw@\vrule\@width\@tempdimb}\hrule}%
}

the "box" has the default thickness of 0.4pt in every style.

score 9 · Answer 2 · answered Nov 12 '20 at 15:44

If your symbols don't have excessive depth (no fractions, for instance), you can get away with

\documentclass{article}
\usepackage{amsmath,array}
\makeatletter
\newcommand{\segment}[1]{%
  \big\lceil\colas@segment{#1}\big\rceil
}
\newcommand{\colas@segment}[1]{%
  \mspace{-4.85mu}%
  \underline{\mspace{5mu}#1\vphantom{j}\mspace{5mu}}%
  \mspace{-4.85mu}%
}
\makeatother
\begin{document}
\Huge
\indent\rlap{\vrule height0pt depth0.1pt width 4cm}%
$\segment{a,b}={ta+(1-t)b: t\in[0,1]}$
\indent\rlap{\vrule height0pt depth0.1pt width 4cm}%
$\segment{p,q}={tp+(1-t)q: t\in[0,1]}$
\end{document}

New symbol derived from [a, b]

2 Answers2