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I'm trying to get a big cross which I can subscript in order to denote a generalized cartesian product (much like how \bigcup works for generalized unions). How can I accomplish this?

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Welcome to TeX.SX! –  ℝaphink Sep 11 '11 at 22:45
    
Have you tried to find the symbol on detexify? Something like \bigotimes without the 'O' maybe? –  ℝaphink Sep 11 '11 at 22:46
    
@Raphink: Thanks! Yes, I tried both things. ´\bigtimes´ isn't defined, and ´\bigotimes´ produces a cross inscribed inside a circle. –  Fernando Martin Sep 11 '11 at 23:20
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Isn't the standard(ish) mathematical notation to use \prod for n-ary Cartesian products, not a giant \times? –  jwodder Sep 12 '11 at 2:07
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6 Answers 6

up vote 13 down vote accepted

Looking in the The Comprehensive LaTeX Symbol List reveals a \bigtimes symbol defined by the mathabx package.

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I just found out (accidentally :)) that the \bigtimes symbol is also defined in the mathtools package. –  Count Zero Sep 12 '11 at 13:45
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regarding mathabx beware that it changes the shape of many other symbols; it is recommended to extract the code for just the desired symbol(s) into your preamble to avoid unexpected results. –  barbara beeton Sep 12 '11 at 13:57
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If you don't mind using a different font, kpfonts gives you the \varprod command:

\documentclass{article}
\usepackage{kpfonts}

\begin{document}

$\varprod_{i=1}^n A_i$

\[
  \varprod_{i=1}^n A_i
\]

\end{document}

enter image description here

I would be more inclined to use \prod to denote a generalised cartesian product, though.

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Strictly speaking, \prod should be the general symbol for product in categorical sense. The Cartesian product is a product in many categories such as sets and modules, but it is not always the case. –  ashpool May 4 at 18:44
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I am sure others will come up with simpler solutions, but here is an overkill solution that might be useful:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\newcommand{\Cross}{\mathbin{\tikz [x=1.4ex,y=1.4ex,line width=.2ex] \draw (0,0) -- (1,1) (0,1) -- (1,0);}}%
\begin{document}
$A \Cross B$
\end{document}

enter image description here

Adjust the x= and y= options to change the size, and the line width= to adjust the thickness of the line. The \mathbin ensures that correct spacing for a binary operator is placed around the symbol.

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If you are down voting, it would be helpful it your provided some explanation so others can know what is wrong with this solution, or why you are opposed to this solution. –  Peter Grill Feb 19 '13 at 19:41
    
I'm not the downvoter, but you seem to be re-implementing the binary cartesian product symbol, and the OP is asking about a "sigma-style" symbol to apply to the Cartesian product of a family of sets. –  Matthew Leingang Mar 27 '13 at 0:29
    
@MatthewLeingang: Ahhh thanks. That clarifies things. –  Peter Grill Mar 27 '13 at 0:43
    
Still, I wouldn't have downvoted. I got to this answer from your comments on tex.stackexchange.com/questions/104164/… and I agree with your POV. –  Matthew Leingang Mar 27 '13 at 1:17
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There is a simple command for that in the mathabx package:

\documentclass{minimal}

\usepackage{mathabx}

\begin{document}
   $\bigtimes\limits_{x=1}$
\end{document}

In fact if you find another operator symbol you fancy, you can try the \limits command on it. It may actually work. :)

I hope this answers it. :)

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If you can use unicode-math, the symbol you are looking for is at U+2A09 'N-ARY TIMES OPERATOR'

\begin{equation}
B ⊂ ⨉_{x∈J}A(x)
\end{equation}

Result of the above code

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Might I suggest a very simple-minded approach?
Why not just use the letter "X"? Below, I inserted \sf to render the symbol more distinguishable

$${\sf X}^n_{i=1} A_i = A_1\times \cdots \times A_n$$
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