Extensible double angle, etc

Question

I was wondering about an efficient way to generate an inner product symbol like

\[
\langle\langle u, v \rangle\rangle
\]

(i.e., double angle brackets), or a norm symbol like

\[
\lvert\lVert x \rVert\rvert
\]

(i.e., triple bars). Of course, the above examples are terrible, no respect for spaces. Is there an efficient way of doing this so that the delimiters are extensible (compatible with $\left$ and $\right$ )?

I know of the package nath, but it's quite incompatible with amsmath, and generates thousands of errors, so is not an option. I've also tried with "DeclareMathDelimiterX" in mathmode, but couldn't get it to work quite as well as I'ld like.

You can try \llangle and \rrangle from the mnsymbol package for the first one. — Martin Tapankov, Mar 02 '11 at 13:33
@MartinTapankov, just a remark: for me, the package is MnSymbol. — Sigur, Aug 16 '12 at 14:34
See also answers in: math mode - How to get double angle bracket without using MnSymbol package? - TeX - LaTeX Stack Exchange — user202729, Dec 17 '21 at 05:37

score 18 · Answer 1 · edited Dec 30 '22 at 16:36

18

Strangely enough, Detexify didn't help here. Another great source is The Comprehensive LaTeX Symbol List, and this has the following answers:

For your first delimiter pair, use \llangle and \rrangle from the MnSymbol package (as observed in Martin's comment above). For the second pair, you can try \vvvert from mathabx.

edited Dec 30 '22 at 16:36

Saibot

205
2
8

answered Mar 02 '11 at 13:40

Hendrik Vogt

37,935

1

I've been writing an answer of my own, but you beat me to it :-) Also somewhat of an option is \interleave from stmaryrd, with the caveat that the spacing around it is all wrong (no left and right versions) – Martin Tapankov Mar 02 '11 at 13:44
1

Sorry, @Martin. You shouldn't have started with a comment :-) – Hendrik Vogt Mar 02 '11 at 13:45
you should it report to Daniel Kirsch. Then he can improve his script, that it finds the \llangle – Mar 02 '11 at 15:58
@Herbert: Done :-) – Hendrik Vogt Mar 02 '11 at 16:12
MnSymbol conflicts with the physics package :/ How can I just get the \llangle and \rangle without having everything break? – Atcold Mar 22 '23 at 18:56

Evpok · Answer 2 · 2013-01-09T02:05:45.147

You might want to try unicode-math with an appropriate font, since Unicode has ⟪double angles⟫ and ⦀triple bars⦀. So you can write \left⦀ or \right⟫, no need for ugly hacks and the spacing is right. And for extra sugar you can use mathtools with it, e.g.

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{unicode-math}
    \setmathfont{XITS Math}
\DeclarePairedDelimiterX\innprod[2]{⟪}{⟫}{#1\delimsize|#2}

\begin{document}
$\innprod*{\frac{a}{ξ}}{b}$
\end{document}

Result of the aforementionned code

score 6 · Answer 3 · answered Mar 02 '11 at 14:36

previous answers for \llangle and \rrangle are good.

this code for triple verts gets good results, although it's a bit of a hack:

\makeatletter
\def\@tvsp{\mathchoice{{}\mkern-4.5mu}{{}\mkern-4.5mu}{{}\mkern-2.5mu}{}}
\def\ltrivert{\left|\@tvsp\left|\@tvsp\left|}
\def\rtrivert{\right|\@tvsp\right|\@tvsp\right|}
\makeatother

using \left and \right with \interleave might also work well; never tried it, since we needed these symbols before the stmaryrd font was available.

Extensible double angle, etc

3 Answers3

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