How can I obtain the braces shown in the below picture?

Question

I am in need to input a certain type of braces to my report and I am not able to find it in latex. Can Somebody help me with this?. I have included a picture of it. Have alook at it.

Answer 1

You also can use \ldbrack and \rdbrack from mathabx, which match nicely the default Computer Modern or Latin Modern fonts. The code below shows how to use them without replacing all maths fonts:

\documentclass{article}
\usepackage{mathtools}

\DeclareFontFamily{U}{matha}{\hyphenchar\font45}
\DeclareFontShape{U}{matha}{m}{n}{ <-6> matha5 <6-7> matha6 <7-8>
matha7 <8-9> matha8 <9-10> matha9 <10-12> matha10 <12-> matha12 }{}
\DeclareSymbolFont{matha}{U}{matha}{m}{n}
%
\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{ <-6> mathx5 <6-7> mathx6 <7-8>
mathx7 <8-9> mathx8 <9-10> mathx9 <10-12> mathx10 <12-> mathx12 }{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}

\DeclareMathDelimiter{\ldbrack} {4}{matha}{"76}{mathx}{"30}
\DeclareMathDelimiter{\rdbrack} {5}{matha}{"77}{mathx}{"38}

\begin{document}

    \[ \bigl\ldbrack\dot x \bigr\rdbrack = \text{some equation} \]

\end{document} 

This being said, other math fonts have defined such delimiters:

• MnSymbol, under the names of \lsem + \rsem,
• fourier has \llbrack+\rrbrack,
• fdsymbol and stix have \lBrack+\rBrack,

and possibly some more which I'm not familiar with.

Answer 2

Try double square bracket \llbracket and \rrbracket from \usepackage{stmaryrd}

\llbracket x \rrbracket

Hope this helps.

Answer 3

When facing such a problem I mostly look at:

The Comprehensive LATEX Symbol List

or at

detexify - LaTeX handwritten symbol recognition,

For example, you can get the symbol in textmode by:

\usepackage{textcomp}
\textlbrackdbl

or in mathmode:

\usepackage{stmaryrd}
\llbracket