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Consider

 $$\left( a_1, a_2, \cdots a_m \right) \mapsto a_1 + \frac{1}{a_2 + \frac{1}{\cdots + \frac{1}{a_m}}}$$

I want to change the cdots into three dots like the following

dot
space dot
space space dot

(Can't find the words to describe this in English.)

Question: Is there an easy way to do this?

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1  
The word is probably 'diagonal'. –  N.N. Aug 27 '11 at 11:23
    
What do you mean with "magnified of course"? –  N.N. Aug 27 '11 at 12:04
    
Removed that to prevent Babylonian type of comms. ;-) –  ndroock1 Aug 27 '11 at 13:41
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2 Answers

up vote 3 down vote accepted
  1. Use \ddots for diagonal dots (see §3.12. "Punctuation" in Short Math Guide for LaTeX).

  2. Also consider to use \cfrac for continued fractions (see §5.4. "Continued fractions" in Short Math Guide for LaTeX).

\documentclass{article}

\usepackage{amsmath}% For \cfrac in the second example

\begin{document}

\[% Here I've just changed the second occurence of \cdots to \vdots
\left( a_1, a_2, \cdots a_m \right) \mapsto a_1 + \frac{1}{a_2 + \frac{1}{\ddots \, + \frac{1}{a_m}}}
\]

\[% \cfrac instead of \frac . This looks much better!
\left( a_1, a_2, \cdots a_m \right) \mapsto a_1 + \cfrac{1}{a_2 + \cfrac{1}{\ddots \, + \cfrac{1}{a_m}}}
\]

\end{document}

Equations with diagonal dots

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1  
Consider using the amsmath command \cfrac for continued fractions. –  You Aug 27 '11 at 12:03
    
@You Great advice! I've updated my answer accordingly. –  N.N. Aug 27 '11 at 12:18
    
Considering I leech MathJax ( I use Blogger ) which slows down MathJax a bit, adding amsmath makes it really slow. But I'll definitely use cfrac when producing pdf documents. –  ndroock1 Aug 27 '11 at 13:36
    
The /ddots was what I was looking for. Thank you. –  ndroock1 Aug 27 '11 at 13:37
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\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\left( a_1, a_2, \cdots a_m \right) \mapsto a_1 
   + \dfrac{1}{a_2 
   + \dfrac{1}{\mkern10mu\raisebox{-0.25\height}{$\ddots$} 
   + \dfrac{1}{a_m}}} 
\]

\end{document}

enter image description here

  • \dfrac is the same as displaystyle\frac
  • \mkern reserves space in math units (1mu=1/18 em)
  • \raisebox is self explanatory
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Interesting. Could you please include what you're doing here? E.g. a short description of \dfrac, \mkern and \raisebox? –  N.N. Aug 27 '11 at 11:15
    
Maybe Herbert thought I could not use ddots ? - I wasn't even aware of the command before today. - Thanks for answering. –  ndroock1 Aug 27 '11 at 13:40
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