Cfrgtkky

I would like to have commands for left- and right gauss brackets which have a double vertical line, but otherwise behave exactly like lfloor and rfloor. In particular, they should come in various sizes and other things should stay unchanged.

I found two candidates, which are both not optimal, unfortunately:

• llfloor and rrfloor in the package stmaryrd. Unfortunately they do not understand preceeding left and right commands. My impression is they are fixed size.




• lFloor and rFloor in the package nath. They come in different sizes, but the problem is that including the package nath introduces automatic sizing behaviour of all symbols of parantheses-type. This might be interesting, but for the moment this change is just too radical for my taste.

Thanks to Werner for providing a solution for this similar question.

A rather quick fix using scalerel would be the following.

Conveniently, scalerel provides scaleleftright[<max width>]{<left obj>}{<stuff>}{<right obj>} (and a comparable stretchleftright) for scaling/stretching both <left obj> and <right obj> to the height of <stuff> (constrained, if required and optional, to a width of <max width>). Here's a quick example:

documentclass{article}

usepackage{scalerel, stmaryrd} % http://ctan.org/pkg/scalerel



newcommand{gaussbracket}[1]{stretchleftright{llfloor}{#1}{rrfloor}}



begin{document}

[ gaussbracket{displaystylesum_{i=1}^n i} ]

end{document}

An option if you don't want to use any packages other than amsmath would be to place two lfloors next to each other with a little negative space between:

This has the advantage of not thickening the horizontal portion of the delimiter.

documentclass{article}

usepackage{amsmath}



newcommand{gaussbr}[1]{%

    leftlfloorhspace{-.33em}leftlfloor #1rightrfloorhspace{-.33em}rightrfloor%

    }



begin{document}



[

gaussbr{A}gaussbr{sum_{n=0}^{infty}a_n}

]



end{document}

Of course, you can adjust the amount of negative space to your liking.