[Tex/LaTex] Bijection, arrow position

positioning

How can I adjust the following arrows such that the arrow heads of longmapsto and longmapsfrom are in accordance with those ones of longleftrightarrow?

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\begin{document}

\begin{align*}
    A &\longleftrightarrow B\\
    a &\longmapsto b \\
    a &\longmapsfrom b
\end{align*}

\end{document}

I just want to place \longmapsto a little bit more to the right. The third arrow is in accordance with the first one, but the second arrow is not. I would like to try out a solution without changed arrow lengths. I just want the output almost as in my example, with the only difference that the second arrow should be positioned a little bit more to the right such that the arrow head is exactly below the arrow head above.

Alternatively, I can define

\begin{align*}
A \longleftrightarrow{}& B\\
a \longmapsto{}& b \\
a \longmapsfrom{}& b
\end{align*}

but then I get the roles interchanged. The second arrow is now in accordance with the first one, but the third is not.

How can I solve this problem?

Best Answer

The arrow heads are the same; the stems have different length, though.

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\let\longleftrightarrow\relax % undefine the command to avoid a warning
\DeclareRobustCommand{\longleftrightarrow}{\leftarrow\bigjoinrel\rightarrow}
\newcommand\bigjoinrel{\mathrel{\mkern-7mu}}

\begin{document}

\begin{align*}
  A &\longleftrightarrow B\\
  a &\longmapsto b \\
  a &\longmapsfrom b
\end{align*}

\end{document}

A more refined definition, so that the difference in length is negligible also in subscripts/superscripts

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\let\longleftrightarrow\relax
\DeclareRobustCommand{\longleftrightarrow}{\leftarrow\bigjoinrel\rightarrow}
\newcommand\bigjoinrel{\mathrel{\mkern-6.78mu\nonscript\mkern-0.22mu}}

\begin{document}

\begin{align*}
  A &\longleftrightarrow B\\
  a &\longmapsto b \\
  a &\longmapsfrom b
\end{align*}

\end{document}

Alternatively, use some padding:

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\newcommand{\bijpad}{\mathrel{\mkern4mu}}

\begin{document}

\begin{align*}
  A &\longleftrightarrow B\\
  a &\longmapsto\bijpad b \\
  a &\bijpad\longmapsfrom b
\end{align*}

\end{document}

Related Solutions

[Tex/LaTex] Placing footnotes or endnotes at the end of the current paragraph

You may put each paragraph into a minipage, because minipages have their own footnotes:

\documentclass{article}
\usepackage[english]{babel}
\usepackage{blindtext}

\newenvironment{mpar}{\par\noindent\minipage{\linewidth}%
  \setlength{\parindent}{1em}%
}{\endminipage\par\medskip}

\begin{document}
\section{Test}
\blindtext
\begin{mpar}First example.\footnote{A note at the foot of the minipage}
\blindtext\end{mpar}
\begin{mpar}Second example.\footnote{A note at the foot of the minipage}
\blindtext\end{mpar}
\blindtext
\end{document}

Or you may define an environment, that does only copy the footnote feature of minipage:

\documentclass{article}
\usepackage{lipsum}

\makeatletter
\newenvironment{footnotepar}{%
  \par
  \def\@mpfn{mpfootnote}\def\thempfn{\thempfootnote}\c@mpfootnote\z@
  \let\@footnotetext\@mpfootnotetext
}{%
  \ifvoid\@mpfootins\else
    \vskip\skip\@mpfootins
    \normalcolor
    \footnoterule
    \unvbox\@mpfootins
  \fi
  \par\smallskip
}
\makeatother

\begin{document}
\lipsum[1-3]
\begin{footnotepar}Lipsum test:\footnote{lipsum is a
    package}\lipsum[2]\end{footnotepar}
\begin{footnotepar}Another\footnote{Not really another one}
  test:\footnote{This is a lipsum test}\lipsum[3]\end{footnotepar}
\lipsum[4]
\end{document}

[Tex/LaTex] \xrightarrow: position of text over an arrow should be lower

I wrote some functions that allow to lower/raise the text under/above xrightarrow arrows. It seams that the text typeset using these macros is a little wider but it doesn't look too bad ;)

The code required is:

\usepackage{ifthen}
\usepackage{xargs}

\newcommandx{\yaHelper}[2][1=\empty]{%
\ifthenelse{\equal{#1}{\empty}}%
  { \ensuremath{ \scriptstyle{ #2 } } } % no offset
  { \raisebox{ #1 }[0pt][0pt]{ \ensuremath{ \scriptstyle{ #2 } } } }  % with offset
}

\newcommandx{\yrightarrow}[4][1=\empty, 2=\empty, 4=\empty, usedefault=@]{%
  \ifthenelse{\equal{#2}{\empty}}
  { \xrightarrow{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's no text below
  { \xrightarrow[ \protect{ \yaHelper[ #2 ]{ #1 } } ]{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's text below
}

\newcommandx{\yleftarrow}[4][1=\empty, 2=\empty, 4=\empty, usedefault=@]{%
  \ifthenelse{\equal{#2}{\empty}}
  { \xleftarrow{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's no text below
  { \xleftarrow[ \protect{ \yaHelper[ #2 ]{ #1 } } ]{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's text below
}

\newcommandx{\yRightarrow}[4][1=\empty, 2=\empty, 4=\empty, usedefault=@]{%
  \ifthenelse{\equal{#2}{\empty}}
  { \xRightarrow{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's no text below
  { \xRightarrow[ \protect{ \yaHelper[ #2 ]{ #1 } } ]{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's text below
}

\newcommandx{\yLeftarrow}[4][1=\empty, 2=\empty, 4=\empty, usedefault=@]{%
  \ifthenelse{\equal{#2}{\empty}}
  { \xLeftarrow{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's no text below
  { \xLeftarrow[ \protect{ \yaHelper[ #2 ]{ #1 } } ]{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's text below
}

Usage is: yrightarrow[<TEXT-BELOW>][<OFFSET-BELOW>]{<TEXT-ABOVE>}[<OFFSET-ABOVE>} and similarly for the others.
A working minimal example looks like this:

\documentclass{minimal}
\usepackage{amsmath}
\usepackage{ifthen}
\usepackage{xargs}

\newcommandx{\yaHelper}[2][1=\empty]{%
\ifthenelse{\equal{#1}{\empty}}%
  { \ensuremath{ \scriptstyle{ #2 } } } % no offset
  { \raisebox{ #1 }[0pt][0pt]{ \ensuremath{ \scriptstyle{ #2 } } } }  % with offset
}   

\newcommandx{\yrightarrow}[4][1=\empty, 2=\empty, 4=\empty, usedefault=@]{%
  \ifthenelse{\equal{#2}{\empty}}
  { \xrightarrow{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's no text below
  { \xrightarrow[ \protect{ \yaHelper[ #2 ]{ #1 } } ]{ \protect{ \yaHelper[ #4 ]{ #3 } } } } % there's text below
}

\begin{document}
    \begin{align*}
        A \yrightarrow{\pi \, \text{s.d.r.}}[-2pt] B \, , \: C \yrightarrow[\pi \, \text{s.d.r.}][4pt]{\pi \, \text{s.d.r.}}[-2pt] D
    \end{align*}
\end{document}

Example Result (Cutout)

However, this seems to be a brute force approach and I don't know whether there may be any side-effects (also I'm not doing any math-size checks, the stuff above and below the arrow will be always set in scriptstyle). And of course it is a "dumb" solution because one has to determine the offset manually. And finally there's no support for the feature suggested by the fifth image.

I'd advise you to accept this answer not (yet) because I hope that somebody can provide a better solution (hopefully including the feature suggested by the fifth image, which possibly could be achieved by printing first the content with a slightly larger font and white colour and then overprint the actual content in black).

Best Answer

Related Solutions

[Tex/LaTex] Placing footnotes or endnotes at the end of the current paragraph

[Tex/LaTex] \xrightarrow: position of text over an arrow should be lower

Related Question