# How to define multiple functions in the same diagram?

I want to write something like this:

So far I tried with tikzcd, but I did not manage to give the arrows the right placement and length.

• Welcome to TeX.SE! Could you please add a minimal example of what you tried so far? Feb 13, 2019 at 13:34

# Solution 1

I would do

\documentclass{article}
\usepackage{amsmath} % \xleftarrow, \xrightarrow
\usepackage{stmaryrd} % \mapsfrom
\begin{document}
$\begin{array}{ccccc} A & \xleftarrow{f} & B & \xrightarrow{g} & C\\ f(x) & \mapsfrom & x & \mapsto & g(x) \end{array}$
\end{document}


You can improve this solution by using Segletes' awesome answer.

# Solution 2 (better IMHO)

However, one can have another solution using TikZ. Pros: you can change the size of the arrow; Cons: the code is longer.

\documentclass[tikz,margin=3mm]{standalone}
\usetikzlibrary{decorations.markings,positioning}
\begin{document}
\begin{tikzpicture}[decoration={
markings,
mark={at position 0 with {\arrow{|}}}}
]
\node (B) {$B$};
\node [left=1.5cm of B.west] (A) {$A$};
\node [right=1.5cm of B.east] (C) {$C$};
\node [below=0.5cm of B.south] (x) {$x$};
\node [left=1.5cm of x.west] (f) {$f(x)$};
\node [right=1.5cm of x.east] (g) {$g(x)$};
\draw[postaction={decorate},->] (x)--(f);
\draw[postaction={decorate},->] (x)--(g);
\draw[->] (B)--(A) node[midway,above] {$f$};
\draw[->] (B)--(C) node[midway,above] {$g$};
\end{tikzpicture}
\end{document}


Edit 1 for Solution #2

Do you mean something like this?

\documentclass[tikz,margin=3mm]{standalone}
\usetikzlibrary{decorations.markings,positioning}
\begin{document}
\begin{tikzpicture}[
decoration={
markings,
mark={at position 0 with {\arrow{|}}}},
every node/.style={rectangle,minimum height=.75cm}
]
\node (B) {$d(M,N)=\sqrt{(x_M-x_N)^2+(y_M-y_N)^2}$};
\node [left=1.5cm of B.west] (A) {$a^2+b^2=c^2$};
\node [right=1.5cm of B.east] (C) {$E=mc^2$};
\node [below=0.5cm of B.south] (x) {$x$};
\node [below left=0.5cm and 0pt of A.south east] (f) {$f(x)$};
\node [below right=0.5cm and 0pt of C.south west] (g) {$g(x)$};
\draw[postaction={decorate},->] (x)--(f);
\draw[postaction={decorate},->] (x)--(g);
\draw[->] (B)--(A) node[midway,above=-1ex] {\scriptsize $f$};
\draw[->] (B)--(C) node[midway,above=-1ex] {\scriptsize $g$};
\end{tikzpicture}
\end{document}


Edit 2 for Solution #2

This is even better IMHO

\documentclass[tikz,margin=3mm]{standalone}
\usetikzlibrary{decorations.markings,positioning}
\begin{document}
\begin{tikzpicture}[
decoration={
markings,
mark={at position 0 with {\arrow{|}}}
},
every node/.style={rectangle,minimum height=.75cm}
]
\node (B) {$d(M,N)=\sqrt{(x_M-x_N)^2+(y_M-y_N)^2}$};
\node [left=1.5cm of B.west] (A) {$a^2+b^2=c^2$};
\node [right=1.5cm of B.east] (C) {$E=mc^2$};
\node [below=0.5cm of B.south] (x) {$x$};
\node [below left=0.5cm and 0pt of A.south east] (f) {$f(x)$};
\node [below right=0.5cm and 0pt of C.south west] (g) {$g(x)$};
\node [below right=0.5cm and 0pt of B.south west] (xl) {};
\node [below left=0.5cm and 0pt of B.south east] (xr) {};
\draw[postaction={decorate},->] (xl)--(f);
\draw[postaction={decorate},->] (xr)--(g);
\draw[->] (B)--(A) node[midway,above=-1ex] {\scriptsize $f$};
\draw[->] (B)--(C) node[midway,above=-1ex] {\scriptsize $g$};
\end{tikzpicture}
\end{document}


• Thanks, I tried both ways. Since in the actual diagram I need, $A,B$ are quite long expressions, when using tikz, the arrows do not start at the same point. Is there a way to change this? Feb 13, 2019 at 14:35
• @klirk Could you explain it further? Do you want to have the arrows aligned? A minimal working example is of great help here!
– user156344
Feb 13, 2019 at 14:49
• I want the arrow to be aligned yes. Alligned at the start and at the end. So their length will differ. Feb 13, 2019 at 15:25
• @klirk Check my edited answer.
– user156344
Feb 13, 2019 at 15:36
• @CarLaTeX Thanks you (and marmot) very much ;-) In fact I have never learnt (or even attempted to learn) packages based on TikZ, like tikz-cd or circuitikz, but for a year I have been drawing many com­mu­ta­tive di­a­grams and electrical networks for my teacher (and in some answer on TeX.SE) quite well :) But maybe when I have some free-time I should start reading those packages' documentations, because it's time to do it ;-)
– user156344
Feb 14, 2019 at 7:47

You can use tabstackengine to get the proper math spacings and align the operators.

\documentclass{article}
\usepackage{amsmath} % \xleftarrow, \xrightarrow
\usepackage{stmaryrd} % \mapsfrom
\usepackage{tabstackengine}
\TABstackMath
\setstacktabulargap{0pt}
\TABbinary
\begin{document}
$\tabularCenterstack{rrcll}{ A & \xleftarrow{f} & B & \xrightarrow{g} & C\\ f(x) & \mapsfrom & x & \mapsto & g(x) }$
\end{document}


If vertical alignment of the relational operators is not a requirement, a simple stack will do:

\documentclass{article}
\usepackage{amsmath} % \xleftarrow, \xrightarrow
\usepackage{stmaryrd} % \mapsfrom
\usepackage{tabstackengine}
\stackMath
\begin{document}
$\Centerstack{ A \xleftarrow{f} B \xrightarrow{g} C\\ f(x) \mapsfrom x \mapsto g(x) }$
\end{document}


You don't really need tikz-cd for that – a simple alignat will do:

\documentclass{article}

\usepackage{amsmath, stmaryrd}
\usepackage{makebox}

\begin{document}

\begin{alignat*}{2}
A & \xleftarrow{\makebox[10pt]{$\scriptstyle f$}} B & & \xrightarrow{\makebox[10pt]{$\scriptstyle g$}} C \\
f(x) & \longmapsfrom \makebox*{$B$}{$x$} & & \longmapsto g(x)
\end{alignat*}

\end{document}


True, one does not need tikz-cd for that, but there is definitely nothing wrong with using it here.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
$\begin{tikzcd}[row sep=0.2em] A & \arrow[l,"f" swap] B \arrow[r,"g"] & C \\ f(x) & \arrow[l,mapsto] x \arrow[r,mapsto] & g(x) \\ \end{tikzcd}$
\end{document}


The same as marmot's answer, but with different column alignment.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
$\begin{tikzcd}[row sep=.5ex, column sep=1.5em, /tikz/column 1/.append style={nodes={anchor=base east}}, /tikz/column 3/.append style={nodes={anchor=base west}}] A & \arrow[l,"f" swap] B \arrow[r,"g"] & C \\ f(x) & \arrow[l,mapsto] x \arrow[r,mapsto] & g(x) \\ \end{tikzcd}$
Or another alternative:
$\begin{tikzcd}[row sep=.5ex, column sep=1.5em, /tikz/column 1/.append style={nodes={text width=width("f(x)"), text centered}}, /tikz/column 3/.append style={nodes={text width=width("g(x)"), text centered}}] A & \arrow[l,"f" swap] B \arrow[r,"g"] & C \\ f(x) & \arrow[l,mapsto] x \arrow[r,mapsto] & g(x) \\ \end{tikzcd}$
\end{document}