# How to bend a mathematical formula around an arc or circle

i would like to bend a math formula around a circle. While it is working with text, LaTeX would not bend a formula in a math environment around a circle, at least, i hadn´t had success. The following code i wrote for a test:

\documentclass[convert={density=300,size=1080x800,outext=.png}]{standalone}
\usepackage{fontspec}
\usepackage{amssymb}
\usepackage{unicode-math}
\usepackage{xfrac}
\usepackage{tikz}
\usepackage{calc}
\usetikzlibrary{decorations.text,fit,chains,calc,shapes.geometric,intersections}
\usepackage[margin=15mm]{geometry}

\begin{document}
\begin{tikzpicture}
\begin{scope}[shift={(0cm,0cm)}, fill opacity=0.5, mytext/.style={text  opacity=1,font=\large\bfseries}]
% Kreise
\draw[fill=red, draw = black] (0,0) circle (5); % Complex Numbers
\draw[fill=blue!10, draw = black,name path=circle 2] (0,0) circle (4.2);  % Imaginary Numbers
\end{scope}

\draw [ draw opacity=0.1, rotate=120,
postaction={decorate, decoration={raise=-1ex,text along path,reverse path,text align={fit to path stretching spaces},
text={|\ttfamily\huge\color{blue}|Outer\space Space       \space}}}] (0,0) circle (4.6cm);
\draw [draw opacity=0.1, rotate=180,
postaction={ decorate, decoration={raise=-1ex,text along path,reverse path,text align={fit to path stretching spaces},
text={|\ttfamily\huge\color{green}|Inner\space Space \space}}}] (0,0) circle (3.8cm);

\node at (4,0) (N) {\tiny 1,2,3,4};
\node[rotate=90] at (-3,1) (N) {$y(n)=h_0x(n)+h_1x(n-1)+\dots +h_{N-1}x(n-N+1)=\sum_{k=0}^{N-1}h_kx(n-k)$};
\end{tikzpicture}

\end{document}

The following result is generated, but the math formular is not bended.

• The accepted answer here may help: tex.stackexchange.com/questions/82867/… – Ethan Bolker Apr 26 '16 at 15:47
• off-topic: I'd use \dots instead of \ldots between the plus signs. – Sigur Apr 26 '16 at 17:33
• @Sigur, this formula was only an arbitrary example for the problem. Anyway, you are right, thank you! – Coliban Apr 27 '16 at 5:00
• @Ethan, thank you, for the advice. But that answer uses an own tikzpicture-environment. As i commented also to Alain Mathes, i need a text bending around a path within or relative to a node. – Coliban Apr 27 '16 at 5:20

From the Manual !

• It is only possible to typeset text in math mode under considerable restrictions. Math mode is entered and exited using any character of category code 3 (e.g., in plain TEX this is $). Math subscripts and superscripts need to be contained within braces (e.g., {^y_i}) as do commands like \times or \cdot. However, even modestly complex mathematical typesetting is unlikely to be successful along a path (or even desirable). \documentclass{article} \usepackage{tikz} \usetikzlibrary{decorations.text} \begin{document} \begin{tikzpicture}[decoration={text along path, text={$\ \ \ y(n)={h_0}x(n)+{h_1}x(n-1)+{\ldots} +{h_{N-1}}x(n-N+1)={\sum_{k=0}^{N-1}}{h_kx(n-k)}}}] \path [decorate] (0,0) .. controls (0,6) and (9,6) .. (9,0); \end{tikzpicture} \end{document} Update \documentclass[margin=1cm]{standalone} \usepackage{fontspec} \usepackage{amssymb} \usepackage{unicode-math} \usepackage{xfrac} \usepackage{tikz} \usepackage{calc} \usetikzlibrary{decorations.text,fit,chains,calc,shapes.geometric,intersections} \begin{document} \begin{tikzpicture}[ disk 1/.style={fill=red, draw = black}, disk 2/.style={fill=blue!10, draw = black,name path=circle 2}, disk 3/.style={ rotate = -90, postaction = % {decorate, decoration={raise = -1ex, text along path, reverse path, text align = {fit to path stretching spaces}, text = {|\ttfamily\huge\color{blue}| Outer\space Space \space}}}}, disk 4/.style={ draw opacity=0.1, rotate=15, postaction={decorate, decoration={ raise=-1ex, text along path, reverse path, text align={fit to path stretching spaces}, text={% |\color{red}|y(n)={h_0}x(n)+{h_1}x(n-1)+{\cdots}+%
{h_{N-1}}x(n-N+1)={\sum_{k=0}^{N-1}}{h_k}x(n-k)\$ }
}
}
}
]
\begin{scope}[  mytext/.style={text  opacity=1,
font=\large\bfseries}]
% Disk 1
\draw[disk 1] (0,0) circle (5);

% Disk 2
\draw[disk 2] (0,0) circle (4.2);
\end{scope}

% Disk 3
\path[disk 3] (0,0) circle (4.6cm);

% Disk 4
\path[disk 4] (0,0) circle (3.8cm);

\end{tikzpicture}
\end{document}

• Beat me by 8 minutes. I will delete my answer! – Steven B. Segletes Apr 26 '16 at 17:32
• Shouldn't cdots be used instead of lots (nice answer btw) – daleif Apr 26 '16 at 19:07
• @daleif I used the formula from the question but yes you are right – Alain Matthes Apr 26 '16 at 19:10
• That´s great, Alain! But it seems, that i am too ignorant to incorporate this. While the bending of the text works flawless within one tikzpicture environment, i had no success in bringing it into a node. But i need a node because i need to implement it in an already existing tikzpicture (and it is rather simpler to position the text inside a bigger picture). Maybe my original question wasn´t that clear, but i need the text to bend it around a node or something. Thank you! – Coliban Apr 27 '16 at 4:49
• Ok, Alain Matthes, thank you very much, i appreciate your work! I can compile your solution in an seperate file, so your solution is the ultimate answer to my question, i accepted your answer. On the other hand, when i incorporate this solution in my original document (a lecture for some mathematics), the processor says "TeX capacity exceeded, sorry" :-), but that is a different story. Thank you very much! – Coliban Apr 27 '16 at 9:22