[Tex/LaTex] Minimum length for \xrightarrow

amsmathlengthssymbols

I want to place text over arrows. The obvious choice is to use the amsmath command \xrightarrow{#1} However, sometimes the text above may be a single digit:

%Example 1
\xrightarrow{1}

other times the text is slightly longer:

%Example 2
\xrightarrow{1000}

The problem I have is that the length of the arrow is scaled to the length of the text. So the arrow in example 1 is much shorter than the arrow in example 2.

Is there a way of making the arrows the same length? Should I use a different command altogether?

Best Answer

In such cases, the command \makebox comes handy. It puts the argument text into a box of customizable width. Even more useful in math mode is \mathmakebox provided by the mathtools package, because it's working better in math mode and respects the current math style.

So, we could start with \xrightarrow{\mathmakebox[3em]{1}}. But we can do better - let's write a macro for that, which produces an arrow of the same width like a text we specify. Here's such a complete example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\newlength{\arrow}
\settowidth{\arrow}{\scriptsize$1000$}
\newcommand*{\myrightarrow}[1]{\xrightarrow{\mathmakebox[\arrow]{#1}}}
\begin{document}
$\myrightarrow{1}$

$\myrightarrow{1000}$
\end{document}

alt text

Related Solutions

[Tex/LaTex] Underarrow with smaller depth, shorter minimum length, and smaller arrow head

I don’t know how much amsmath’s \underleftarrow slows the compilation down or how it would with TikZ, but here is a solution that uses PGF and avoids the parsing process of TikZ.

The proposed solution uses only one \pgfpicture which measured the under-arrowed math content after typesetting it in an box using

\edef\pgf@math@fam{\the\fam}%

and later

\sbox\pgfutil@tempboxa{$\fam\pgf@math@fam#1#2$}%

where the saved font setting is set again, combined with \mathpalette which forwards the current math style to \@pgfunderleftarrow.

The box’s width is stored in \pgfutil@tempdimb which is then used in drawing the line (where we have used \wd\pgfutil@tempboxa directly, too).

This makes it possible to let TeX typeset the math content as it is but also measure it as precise as possible. As I realized later, even the original \underleftarrow doesn’t kepp the math family font settings (like \mathsf) so maybe you want to change this again.

This \the\fam trick was provided by egreg in a chat message from 2013-07-31:

For a single symbl it should work.

It seems also to work for more than one symbol.

The original definition of the to arrow is

\pgfarrowsdeclare{to}{to}
{ … }{
  \pgfutil@tempdima=0.28pt%
  \advance\pgfutil@tempdima by.3\pgflinewidth%
  \pgfsetlinewidth{0.8\pgflinewidth}
  \pgfsetdash{}{+0pt}
  \pgfsetroundcap
  \pgfsetroundjoin
  \pgfpathmoveto{\pgfqpoint{-3\pgfutil@tempdima}{4\pgfutil@tempdima}}
  …
}

The important part is the setup of \pgfutil@tempdima as the y value of the \pgfpathmoveto coordinate is 4\pgfutil@tempdima which makes up the vertical height of the arrow. \pgfutil@tempdima in the definition of \@pgfunderleftarrow is used to calculate this height (we cannot extract it from some macro like the left and right extend).

To let the arrow arc touch the bottom of the math content we would use:

\pgfutil@tempdima=0.28pt%
\advance\pgfutil@tempdima by.3\pgflinewidth%
\pgfutil@tempdima-4\pgfutil@tempdima
\advance\pgfutil@tempdima-.4\pgflinewidth

The last line adds half the line width of the arrow line (which is set to 0.8\pgflinewidth).

So why did I do something differently, namely \pgfutil@tempdima=0.28pt% \advance\pgfutil@tempdima by.8\pgflinewidth% \pgfutil@tempdima-4\pgfutil@tempdima

Because I haven’t done it right (.5 instead of .4 of the line width added and before the multiplication of the factor 4), but it looks right.

Of course, you can change the factors and addition if you think it looks better.

The unstarred version of \pgfunderleftarrow doesn’t add any depth to the line (other than the depth of the math content itself). If this depth is needed (take a look at a \fraction), the starred version \pgfunderleftarrow* can be used.

Code

\documentclass{article}
\usepackage{amsmath}
\usepackage{pgf}
\makeatletter
\newcommand*{\pgfunderleftarrow}{%
  \@ifstar
    {\let\ifpgf@depth\iftrue\mathpalette\@pgfunderleftarrow}
    {\let\ifpgf@depth\iffalse\mathpalette\@pgfunderleftarrow}%
}
\newcommand*{\@pgfunderleftarrow}[2]{%
  #2%
  \edef\pgf@math@fam{\the\fam}%
  \pgfpicture
    \pgfsetbaseline{0pt}%                 % "baseline = 0pt"
    \pgf@relevantforpicturesizefalse      % "overlay"
    \pgfsetroundcap                       % "line cap = round"
    \pgfsetarrowsend{to}%                 % "arrows = -to"
    \pgfutil@tempdima=0.28pt%
    \advance\pgfutil@tempdima by.8\pgflinewidth%
    \pgfutil@tempdima-4\pgfutil@tempdima
    \sbox\pgfutil@tempboxa{$\m@th\fam\pgf@math@fam#1#2$}%
    \advance\pgfutil@tempdima-\dp\pgfutil@tempboxa
    \pgfutil@tempdimb\wd\pgfutil@tempboxa
    \pgfpathmoveto{\pgfqpoint{0pt}{\pgfutil@tempdima}}%
    \pgfpathlineto{\pgfqpoint{-\pgfutil@tempdimb}{\pgfutil@tempdima}}%
    \pgfusepath{stroke}%                  % "draw"
    \ifpgf@depth
      \pgf@relevantforpicturesizetrue
      \pgfpathmoveto{\pgfqpoint{0pt}{-\pgfutil@tempdimb}}%
      \pgfusepath{use as bounding box}%
    \fi
  \endpgfpicture
}
\makeatother
\begin{document}
\begin{gather*}
  \mathsf{bit_0} \bullet \underleftarrow{\mathsf{inc}} \\
  \mathsf{bit_1} \bullet \underleftarrow{\mathsf{p}}  \\
  \mathsf{bit_2} \bullet \underleftarrow{\mathsf{f}} \\
  \mathsf{bit_2} \bullet \mathsf{\underleftarrow{f}} \rlap{$\to$ \texttt{\char`\\mathsf} lost?}
\end{gather*}
\begin{gather*}
  \mathsf{bit_0} \bullet \pgfunderleftarrow{\mathsf{inc}} \bullet \mathsf{\pgfunderleftarrow{inc}}\\
  \mathsf{bit_1} \bullet \pgfunderleftarrow{\mathsf{p}} \bullet \mathsf{\pgfunderleftarrow{p}}\\
  \mathsf{bit_2} \bullet \pgfunderleftarrow{\mathsf{f}} \bullet \mathsf{\pgfunderleftarrow{f}}
\end{gather*}
\begin{equation*}
  \frac{\pgfunderleftarrow*{f}}{f} \neq \frac{\pgfunderleftarrow{f}}{f} \neq \frac{\underleftarrow{f}}{f}
\end{equation*}
\end{document}

Output

Original `\underleftarrow` (last line uses `\mathsf{\pgfunderleftarrow{f}}`)

enter image description here

PGF version

enter image description here

[Tex/LaTex] How to draw a labeled triple arrow (\Rrightarrow)

You're lucky: \equiv and \Rrightarrow can be combined.

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\xRrightarrow}[2][]{\ext@arrow 0359\Rrightarrowfill@{#1}{#2}}
\newcommand{\Rrightarrowfill@}{\arrowfill@\equiv\equiv\Rrightarrow}
\newcommand{\xLleftarrow}[2][]{\ext@arrow 3095\Lleftarrowfill@{#1}{#2}}
\newcommand{\Lleftarrowfill@}{\arrowfill@\Lleftarrow\equiv\equiv}
\makeatother

\begin{document}

$A\xRrightarrow{fghi}B$

$A\xLleftarrow{fghi}B$

\end{document}

One can also add the symmetric version:

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\xRrightarrow}[2][]{\ext@arrow 0359\Rrightarrowfill@{#1}{#2}}
\newcommand{\Rrightarrowfill@}{\arrowfill@\equiv\equiv\Rrightarrow}
\newcommand{\xLleftarrow}[2][]{\ext@arrow 3095\Lleftarrowfill@{#1}{#2}}
\newcommand{\Lleftarrowfill@}{\arrowfill@\Lleftarrow\equiv\equiv}
\newcommand{\xLleftRrightarrow}[2][]{\ext@arrow 3399\LleftRrightarrowfill@{#1}{#2}}
\newcommand{\LleftRrightarrowfill@}{\arrowfill@\Lleftarrow\equiv\Rrightarrow}
\makeatother

\begin{document}

$A\xRrightarrow{fghi}B$

$A\xLleftarrow{fghi}B$

$A\xLleftRrightarrow{fghi}B$

\end{document}