# How can I rotate \in by 90 degrees?

I am currently trying to show the domain of variables in a simple equation:

$\begin{matrix} x & \cdot & W_{1,2} & = & o\\ \in & & \in & & \in\\ \mdr^{1\times n} & & \mdr^{n \times m} & & \mdr^{1 \times m} \end{matrix}$

There are some more issues with this way to show the domain of variables, but this question is mainly about the rotated \in.

## Failed tries

I've tried \usepackage{rotating}:

$\begin{matrix} x & \cdot & W_{1,2} & = & o\\ \text{\begin{rotate}{-90}\in\end{rotate}} & & \in & & \in\\ \mdr^{1\times n} & & \mdr^{n \times m} & & \mdr^{1 \times m} \end{matrix}$

The result looks like this:

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– egreg Jun 12 '14 at 15:13
You can \def\rin{\rotatebox[origin=c]{-90}{$\in$}} and use \rin instead of \in in your formula. Requires package graphicx – JLDiaz Jun 12 '14 at 15:18
Is this for a presentation with slides or for a paper? – Bordaigorl Jun 12 '14 at 15:27

The result is really ugly:

\documentclass{article}
\usepackage{graphicx,amssymb}
\newcommand{\vin}{\rotatebox[origin=c]{-90}{$\in$}}
\begin{document}
$\begin{array}{@{}c@{\;}c@{\;}c@{\;}c@{\;}c@{}} x & \cdot & W_{1,2} & = & o \\ \vin && \vin && \vin \\ \mathbb{R}^{1\times n} && \mathbb{R}^{n\times m} && \mathbb{R}^{1\times m} \end{array}$
\end{document}

I'd simply avoid such visual description in print; I often use something like that on the blackboard, but it's a completely different situation. I'd prefer something like

$x\cdot W_{1,2} = o$
where $x\in\mathbb{R}^{1\times n}$ and $W_{1,2}\in\mathbb{R}^{n\times m}$.

in a printed document.

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You could try the \usepackage{rotating} package and use the \begin{rotate}{30}...\end{rotate} environment.

Untested - I have to the possibility right now.

Or use the approach described in Rotated $\ltimes$ symbol (\rotatebox command from the graphicx package).

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I've tried it and it looks ugly (see updated question) – Martin Thoma Jun 12 '14 at 15:21
rotating is not the best approach. – egreg Jun 12 '14 at 15:22

Here's an idea for annotating an equation without affecting the spacing and with a clean way of rotating the \in:

\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz}
\usetikzlibrary{positioning}

\def\mdr{\mathbb{R}}

\tikzset{m/.style={inner sep=0, outer sep=0,remember picture}}
\begin{document}
\noindent
$x_0\cdot A^n = o$
\\[1em]
$\tikz[m] \node (x) {$x_0$};\cdot \tikz[m] (a) \node {$A^n$}; = \tikz[m] \node (w) {$o$};$
\begin{tikzpicture}[remember picture,overlay, node distance=.5]
\node[shape=circle, draw=blue,minimum size=1.5em] (xc) at (x) {};
\node[below=of x] (xd) {$\mdr^{1\times n}$};
\path (xc) -- node[sloped] {$\in$} (xd);
\end{tikzpicture}
\end{document}

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