Long equals in tikz

Question

How could I proceed to make an "equal" arrow in a diagram in tikz? To be clearer, what I would like to obtain is the equivalent of the following command in xy:

\ar@{=}[direction]

Two examples of what I want (done in tikz):

and

Thank you for your help.

I guess \draw (a1) edge[bend left,double distance=2pt] (a2); should work, assuming nodes be named... — Claudio Fiandrino, Jun 26 '13 at 10:51
"double distance" works for the equal sign :) Do you know by any chance if there is a way to use something like "to [out = 45, in = -45]" instead of "bend left"? — Daniel Robert-Nicoud, Jun 26 '13 at 10:56

score 18 · Accepted Answer · answered Jun 26 '13 at 12:27

18

You can use double equal sign distance in your \draw options to set the distance between the double lines to match that of an equal sign.

The double lines work with any path specification, including things like bend left or to [out=45]:

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw [double equal sign distance] (0,0) to [out=45, in=180] (3,0) node [anchor=mid west] {$= A$};
\end{tikzpicture}
\end{document}

answered Jun 26 '13 at 12:27

Jake

232,450

Yours answers rock! – juliohm Jun 26 '13 at 13:16
6

Although this is right, I want to gripe pointlessly that the double distance option always produces a faint dark edge across the "gap" at the ends of the path. Presumably this is because the path is drawn first in black and then overdrawn in white (as the manual explains) but it would be nice if they would line up correctly... – Ryan Reich Jun 26 '13 at 22:25

score 15 · Answer 2 · edited Jun 05 '17 at 19:19

The great tikz-cd package (tikz-cd, manual) includes the option equal for arrows.

Code

\documentclass[tikz,convert=false]{standalone}
\usepackage{tikz-cd}
\usetikzlibrary{arrows}
\tikzset{commutative diagrams/.cd,arrow style=tikz,diagrams={>=latex'}}
\begin{document}
\begin{tikzcd}[swap,bend angle=45]
A \dar{f} \rar{a} \ar[bend left,equal]{rr}
  & X \dar{g} \rar{r}
      & A \dar[swap]{f} \\
B \rar[swap]{i}   \ar[bend right,equal]{rr}
      & Y \rar[swap]{\beta}
          & B
\end{tikzcd}
\end{document}

Output

enter image description here

Long equals in tikz

2 Answers2

Code

Output

Linked