how to write a formula that branches into two?

Question

I would like to write a formula (see the picture), how can i fix the arrows?

This is my code:

\documentclass[a4paper,12pt]{article}[12pt] 
\usepackage[italian]{babel} 
\usepackage[T1]{fontenc} 
\usepackage[utf8]{inputenc} 
\usepackage{anysize}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathrsfs} 
\usepackage{textcomp} 
\linespread{1.5}

\frenchspacing 

\newcommand{\abs}[1]{\lvert#1\rvert}

\usepackage{floatflt,epsfig}

\usepackage{multicol}




\usepackage[a4paper,top=1.0cm,bottom=1.0cm,left=1.0cm,right=1.0cm]{geometry}


\begin{document}


$ \dfrac{a \pm b}{c} = \rightarrow  $

$ \dfrac{a+b}{c} $

$ \dfrac{a-b}{c} $




\end{document}

Can I ask a favour please? Thank you to have accepted (check) my answer, but for my opinion is not the best. Good year. — Sebastiano, Jan 02 '19 at 23:40

score 9 · Answer 1 · answered Jan 02 '19 at 15:32

Here is an adapted version from Claudio Fiandrino's answer to Joining parts of equations with lines or arrows using tikz.

\documentclass{article}
\usepackage{tikz}
\usepackage{amsmath}

\begin{document}

\begin{tikzpicture}[grow=right, 
                    sibling distance=50pt,
                    level distance=2cm,
                    edge from parent path={(\tikzparentnode.east) -- (\tikzchildnode.west)},
                    edge from parent/.style={draw,-latex}]
    \node {$ \dfrac{a \pm b}{c} =$}
    child {node {$ \dfrac{a-b}{c} $}}
    child {node {$ \dfrac{a+b}{c} $}}
    ;
\end{tikzpicture}
\end{document}

@ryuk: From the message you quoted, I guess that you copied my code into an existing document that was previously compiled and had used \usepackage[italian]{babel}. To get rid of the error, either recompile or add the above mentioned package back to your preamble. — leandriis, Jan 02 '19 at 15:45

Bernard · Answer 2 · 2019-01-02T23:33:07.550

8

Without using a hammersledge to crack a nut, you already have the necessary packages for the below code.

Unrelated: epsfigure and anysize are obsolete. The functionalities of the former are achieved with graphicx and the latter can be replaced with geometry (which you use, anyway).

\documentclass[a4paper, 12pt]{article}
\usepackage[italian]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[a4paper, margin=1.0cm]{geometry}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{multicol}
\linespread{1.5}
\frenchspacing

\usepackage{old-arrows}

\begin{document}


\[ \dfrac{a \pm b}{c} =
\begin{matrix}
\nearrow \\[-1.5ex] \searrow
\end{matrix}
\:
\begin{matrix}
 \dfrac{a+b}{c} \\[3ex]
 \dfrac{a-b}{c}
\end{matrix} \]

\end{document}

If you want to have the arrows figure centred on the math axis, and control the gap between the arrows, you can replace the matrix environment for the arrows with \Vectorstack from the stackengine package (load it with option [usestackEOL]). Here are two examples, with a different gap:

\[\Lstackgap = 10pt\dfrac{a ± b}{c} =
\Vectorstack{%
\nearrow \\%[-1.5ex]
 \searrow }
\:
\begin{matrix}
 \dfrac{a+b}{c} \\[3ex]
 \dfrac{a-b}{c}
\end{matrix} \]

\[\Lstackgap = 18pt\dfrac{a ± b}{c} =
\Vectorstack{%
\nearrow \\%[-1.5ex]
 \searrow }
\:
\begin{matrix}
 \dfrac{a+b}{c} \\[3ex]
 \dfrac{a-b}{c}
\end{matrix} \]

edited Jan 02 '19 at 23:33

answered Jan 02 '19 at 16:47

Bernard

271,350

Those arrows look uncentered in relation to the equals sign. Would there be any way of fixing that? – AJF Jan 02 '19 at 18:54
Do you mean vertically uncentred? – Bernard Jan 02 '19 at 18:57
Yes, I mean vertically uncentered. The arrows' origins are lower than I visually expect them to be. – AJF Jan 02 '19 at 21:02
1

@AJFarmar: I've posted a variant code, which uses stackengine and is more versatile. Please see if it's OK for you. – Bernard Jan 02 '19 at 21:55
The visual improvement is enormous. Thank you very much. – AJF Jan 02 '19 at 21:56
1

You're welcome. We're here to help, as much as we can. – Bernard Jan 02 '19 at 21:58
@Bernard Good and happy new year. Can you edit your answer. There are two fragments without .'...'. – Sebastiano Jan 02 '19 at 23:23
1

@Sebastiano: I wish you a very happy new year too. As often, I forgot to check if all the code was in the right position. Thank you for pointing it! – Bernard Jan 02 '19 at 23:35

Sebastiano · Accepted Answer · 2019-01-02T23:41:08.240

6

Another simple possibility using tikz-cd.

\documentclass[a4paper,12pt]{article}
\usepackage{tikz-cd}
\usepackage{amsmath}

\begin{document}
\begin{tikzcd}[cells={nodes={minimum height=-2cm,minimum width=1cm}},column sep=3em,row sep=-7pt]
 & \dfrac{a+b}{c}  \\
\dfrac{a \pm b}{c} = \arrow[ru] \arrow[rd] &  \\
 & \dfrac{a-b}{c} 
\end{tikzcd}
\end{document}

edited Jan 02 '19 at 23:41

answered Jan 02 '19 at 16:50

Sebastiano

54,118

how to write a formula that branches into two?

3 Answers3

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