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A kind of dot is sometimes used to represent the sum, mean, or subset of a matrix. What should that symbol be? See the example below:

enter image description here

lindelof
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    e.g., $y_{\bullet\bullet} + (y_{i\bullet} - y_{\bullet\bullet})$ – Steven B. Segletes Apr 05 '17 at 14:14
  • See also our old favourite post: http://tex.stackexchange.com/questions/14/how-to-look-up-a-symbol-or-identify-a-math-symbol-or-character Detexify will find the symbol, but it's not that easy :P – Au101 Apr 05 '17 at 14:27

1 Answers1

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The symbol you seek is \bullet, and then I just put it in an amsmath aligned environment.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
\begin{aligned}
\hat y_{ij} &= \hat\mu +\hat\alpha_i + \hat\beta_j\qquad\qquad 
  (i = 1,\dots. I \text{~et~} j = 1,\dots,J)\\
&= y_{\bullet\bullet} + (y_{i\bullet} - y_{\bullet\bullet})  
+ (y_{\bullet j} - y_{\bullet\bullet})\\
&= y_{i\bullet} + y_{\bullet j} - y_{\bullet\bullet}
\end{aligned}
\]
\end{document}

enter image description here

Steven B. Segletes
  • 237,551