Redefine \middle| to insert space before and after itself

Question

I want to use \middle| inside of brackets like this.

\documentclass{article}
\begin{document}

\begin{equation}
  \left\{\frac{1}{n} \middle| n>0\right\}
\end{equation}

\end{document}

\end{document}

But this examples lacks space before and after the mid |. I don't want to write every time:

left\{\frac{1}{n} \;\middle|\; n>0\right\}

How can I redefine the \middle| command to mean \;\middle|\;? I tried

\edef{\middle|}{\,\middle|\,}

and

\let\originalmiddle\middle
\renewcommand{\middle}{\;\originalmiddle\;}

but neither works. What is the difference between both commands and why do they not work with \middle?

Maybe you just want \mid? Though, that won't scale vertically. — morbusg, Jul 23 '14 at 16:28
I want the middle command to scale vertically like \middle| does. — Marco Breitig, Jul 23 '14 at 16:31
See http://tex.stackexchange.com/q/5502 to get \middle| to behave exactly as \mid — Philippe Goutet, Jul 23 '14 at 16:48

score 8 · Accepted Answer · answered Jul 23 '14 at 16:31

8

The symbol needs to come after the \middle so

\let\originalmiddle\middle
\renewcommand{\middle}[1]{\;\originalmiddle#1\;}

Although redefining primitives always breaks something, somewhere so I would suggest instead

\newcommand{\xmiddle}[1]{\;\middle#1\;}

and use \xmiddle (or any other name you wish)

answered Jul 23 '14 at 16:31

David Carlisle

Wow thx, that was fast! I tried to play around with a parameter but somehow did not manage to get things right. – Marco Breitig Jul 23 '14 at 16:33
Just out of curiosity, do you know how would one do that with a \(U)delcode or \(U)delimiter? (i.e., without \middle?) – morbusg Jul 23 '14 at 16:35
@morbusg If I understand your comment correctly, I don't think you can – David Carlisle Jul 23 '14 at 16:36
I mean, if I wouldn't have \left...\right, but instead \bigl...\bigr, then \middle wouldn't work; but as the | is also defined as a delimiter, one can do \big|, but that isn't a class relation symbol then. I was wondering if that could be made a relation. – morbusg Jul 23 '14 at 16:41
1

@morbusg \bigm|? – Manuel Jul 23 '14 at 16:45
1

@morbusg \bigm \Biggm and friends are defined already to be relation just as \bigr is \mathopen – David Carlisle Jul 23 '14 at 16:45
@Manuel, David: Oooh! I didn't know that! Thanks! – morbusg Jul 23 '14 at 16:48
1

\newcommand{\relmiddle}{\nonscript\;\middle\nonscript\;} – egreg Jul 23 '14 at 17:29

1 Answers1