# Orthogonal direct sum

Several authors use a circled perpendicular sign to indicate orthogonal direct sums.

What is the appropriate way to implement this, so you can use it like \oplus and \bigoplus ?

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possible duplicate of How to look up a symbol? –  Ian Thompson Jul 1 '12 at 20:28
this is a relatively recent addition to unicode (U+2989), and i believe it exists only in the stix/xits fonts. it comes only in one size, so it would have to be enlarged for the \big; a method for doing this is given in the question define-strange-operators –  barbara beeton Jul 1 '12 at 20:56
@IanThompson: By barbara's comment this is no as simple. –  Caramdir Jul 1 '12 at 20:59
@caramdir --- Maybe I'm missing something, but \obot and \bigobot from mathabx look like circled perpendicular signs to me. –  Ian Thompson Jul 1 '12 at 21:01
@Ian: Well, sort of. I guess that is the closes approximation you can get without going the unicode-math route. The Unicode symbol ⦹ U+29B9 (circled perpendicular) is different from ⦺ U+29BA (circle divided by horizontal bar and top half divided by vertical bar). The mathabx symbol is the latter. –  Caramdir Jul 1 '12 at 21:43

To summarize the comments, here are the options currently available.

• The mathabx provides \obot and \bigobot. These symbols look like

If you don't want to include all the mathabx symbols (they overwrite many Computer Modern symbols), then you can use the following setup (taken from Importing a Single Symbol From a Different Font):

\documentclass{article}
% Setup the matha and mathx font (from mathabx.sty)
\DeclareFontFamily{U}{matha}{\hyphenchar\font45}
\DeclareFontShape{U}{matha}{m}{n}{
<5> <6> <7> <8> <9> <10> gen * matha
<10.95> matha10 <12> <14.4> <17.28> <20.74> <24.88> matha12
}{}
\DeclareSymbolFont{matha}{U}{matha}{m}{n}
\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{
<5> <6> <7> <8> <9> <10>
<10.95> <12> <14.4> <17.28> <20.74> <24.88>
mathx10
}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}

\DeclareMathSymbol{\obot}         {2}{matha}{"6B}
\DeclareMathSymbol{\bigobot}       {1}{mathx}{"CB}

\begin{document}
$V \obot W \qquad \bigobot V_i$
\end{document}

• Unicode additionally defines ⦹ U+29B9 (circled perpendicular), but doesn't provide a big counterpart. The symbol can be used with the unicode-math package and LuaLaTeX or XeLaTeX. As of summer 2012 only the XITS and Cambria math fonts include the symbol. In XITS Math it looks like

The corresponding TeX code is

% compile with lualatex
\documentclass{article}
\usepackage{unicode-math}
\setmathfont{XITS Math}

\begin{document}
$V \operp W$
\end{document}


The Unicode also has \obot, looking similar to the example above, but doesn't provide \bigobot. You could try to fake the large symbols with something like {\text{\Large$\operp$}}\limits_{i∈I} V_i, but the scaling will make the symbol heavier:

In general have a look at How to look up a symbol? to see how you can find a specific symbol.

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