# how to write ceil and floor in latex?

Is there a macro in latex to write ceil(x) and floor(x) in short form? The long form

\left \lceil{x}\right \rceil


is a bit lengthy to type every time it is used.

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## migrated from stackoverflow.comJun 7 '13 at 22:41

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Welcome to TeX.SX! Your post was migrated here from another Stack Exchange site. Please register on this site, too, and make sure that both accounts are associated with each other (by using the same OpenID), otherwise you won't be able to comment on or accept answers or edit your question. –  Joseph Wright Jun 8 '13 at 5:31
Thank you, it seems I was asking questions in the wrong forum indeed! –  danny Jul 7 '13 at 17:35

Using \DeclarePairedDelimiter from mathtools, you could define macros \ceil and \floor, which will scale the delimiters properly (if starred):

\documentclass{minimal}
\usepackage{mathtools}
\DeclarePairedDelimiter\ceil{\lceil}{\rceil}
\DeclarePairedDelimiter\floor{\lfloor}{\rfloor}

\begin{document}
\begin{equation*}
\floor*{\frac{x}{2}} < \frac{x}{2} < \ceil*{\frac{x}{2}}
\end{equation*}
\end{document}


Result:

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Doesn't work here. Any idea how to do it without mathtools? –  David 天宇 Wong Mar 5 at 1:54
Just a question: why * when using \floor? I noticed that if the * is omitted from the command, the delimiter does not resize... but why? –  Gherardo Jul 11 at 7:26
@Gherardo: Check the documentation of the mathtools package. It's just the way the \DeclarePairedDelimiter macro works — you can also make it use a specific size if you want to: \floor[\Bigg]{\frac{x}{2}}. –  You Jul 11 at 10:10
1. You can define your own macro via the \def command anywhere in your document. For example

\def\lc{\left\lceil}
\def\rc{\right\rceil}


and then just write \lc x \rc.

2. Or you use the \providecommand in the preamble, e.g.

\providecommand{\myceil}[1]{\left \lceil #1 \right \rceil }


to simply use \myceil{x} in your document.

3. Use an editor, like vim, that allows for defining shortcuts for quick and efficient editing.
\newcommand{\floor}[1]{\lfloor #1 \rfloor}

Welcome to TeX.SX! \floor and \rfloor are amsmath commands, mathtools builds on top of amsmath, so it's no wonder, this would work even without mathtools. The solution with \DeclarePairedDelimiter shows better spacing however. Perhaps you should elaborate on your answer and show some screenshot and a full example, not only fragments of code –  Christian Hupfer Jun 24 at 23:47