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I'm writing up some notes that will be displayed on an overhead projector. The standard time-derivative \dot{x} produces a dot that is hard to see. Does anyone know of a package or have a macro that produces a (nice looking) larger dot? Similarly with \ddot{x}.

At the moment, I've been supplied with some ugly code that produces an ugly output:

\def\dt#1{{\buildrel  {\hbox{\LARGE . }} \over {#1}}}    % dot-over 
\def\ddt#1{{\buildrel {\hbox{\LARGE ..}} \over {#1}}}    % double dot
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4 Answers 4

up vote 10 down vote accepted

You could use the accents package and its command \accentset to create faked accents. Here`s an example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{accents}
\newcommand*{\dt}[1]{%
  \accentset{\mbox{\large\bfseries .}}{#1}}
\newcommand*{\ddt}[1]{%
  \accentset{\mbox{\large\bfseries .\hspace{-0.25ex}.}}{#1}}
\begin{document}
$\dot{x} \neq \dt{x}$

$\ddot{x} \neq \ddt{x}$
\end{document}

Output:

alt text

Instead of a large bold period you could also choose for instance a tiny \bullet.

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The amsmath package provides the commands \overset and \underset to set arbitrary things over/under other arbitrary things. So with amsmath and bm loaded you can use

\overset{\bm .}{a}

to obtain an "a" with a bold dot on it.

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The normal \dot uses the dot accent from the font, so switching font families to a font set with larger accents would be the cleanest solution.

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Can you give an example? Would that also switch the font of the text/math? –  Simon Aug 17 '10 at 8:27
    
No, sorry. I do not use LaTeX myself. Anyway, I think Caramdir's answer is better –  Taco Hoekwater Aug 17 '10 at 9:48
    
For slides, a sans-serif font might be a good idea, and it may help with the dot problem as well. –  Jukka Suomela Aug 17 '10 at 10:39

Maybe rather use \partial_t x or x_t? Also quite compact and much more noticeable.

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I agree, but I'm writing the notes for someone else, so I don't get a say in the matter. –  Simon Aug 17 '10 at 8:26

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