# how to draw double-circle diagram in tiKz?

How can I draw the following diagram in LaTeX? But instead of the black dots in vertices, I want to put the numbers.

• Welcome to TSE. Please post a Minimal Working Example, instead of a code snippet. Commented May 13, 2023 at 8:51
• What did you try so far? Without some example of your code helping out is difficult. Commented May 13, 2023 at 8:53
• Alternatively you can also try things like tools - What GUI applications are there to assist in generating graphics for TeX? - TeX - LaTeX Stack Exchange Commented May 13, 2023 at 9:01
• I have the no code that way I ask you Commented May 13, 2023 at 9:20
• Welcome. // Understandable, but unfortunately the wrong approach for this site. // Suggestion: look up the minimal introduction at ctan, e.g. via your search engine, to get some basic understanding of how Tikz works. Use this sites search box and "Related" links to find something similar, to start adjusting it to your needs. // We appreciate, when you add your attempts as code to your question (via EDIT), to show your achievements and obstacles. That's, when you'll get most out of our answers. // I'm confident, you'll make it :) Commented May 13, 2023 at 10:20

For this one we need the following TikZ libraries:

1. calc to place some nodes at the middle point between another two:
\node (N) at ($(A)!0.5!(B)$) {}; % places the node (N) midway between (A) and (B)

1. backgrounds to draw the ellipses last, but on background layer (behind the nodes). This option needs a scope.

For the rest, first place all the nodes, then draw the lines (as said, on background layer). As the picture has two graphs almost identical, we can use a \foreach loop to place the left and right nodes with the same code, and another one for the the numbered nodes.

Like this:

\documentclass[tikz,border=1.618mm]{standalone}
\usetikzlibrary{calc,backgrounds}

\definecolor{aquamarine}{HTML}{008B9B}
\tikzset{my node/.style={draw,circle,fill=white,inner sep=0,minimum size=9mm}}

\begin{document}
\begin{tikzpicture}
\def\a{4.5}  % a semiaxis
\def\b{2.25} % b semiaxis
\def\h{2.5}  % height
\foreach[count=\jj from 0]\j in {L,R} % left, right
{
\begin{scope}[shift={({2*\jj*(\a+0.5)},0)}]
\foreach[count=\ii]\i in {130,210,250,290,330}
{% nodes 1 to 5
\node[my node]              (\j B\ii) at (\i:\a cm and \b cm) {$\ii'$};
\node[my node,yshift=\h cm] (\j T\ii) at (\i:\a cm and \b cm) {$\ii$};
}% nodes 6 and 7
\node[my node]              (\j B6) at (50:\a cm and \b cm) {};
\node[my node,yshift=\h cm] (\j T6) at (50:\a cm and \b cm) {};
\node[my node]              (\j B7) at (90:\a cm and \b cm) {$(2n)'$};
\node[my node,yshift=\h cm] (\j T7) at (90:\a cm and \b cm) {$(2n)$};
\foreach\i in {1,...,7}% vertical lines
\draw (\j B\i) -- (\j T\i);
\foreach\i in {2,4}% middle height nodes
\node[my node]  at ($(\j B\i)!0.5!(\j T\i)$) {\pgfmathparse{int(\i/2)}$\bar\pgfmathresult$};
\node[rotate=-10] at ($(\j B6) !0.5!(\j T7)$)  {$\cdots$}; % dots
\end{scope}
}
% ellipses
\begin{scope}[on background layer]
\draw[very thick,red]        (0,0)  ellipse (\a cm and \b cm);
\draw[very thick,aquamarine] (0,\h) ellipse (\a cm and \b cm);
\draw[very thick,red]        (RT7) -- (RB1.center) arc (130:450:\a cm and \b cm);
\draw[very thick,aquamarine] (RB7) -- (RT1.center) arc (130:450:\a cm and \b cm);
\end{scope}
\end{tikzpicture}
\end{document}


As the TO is new at least to Tikz, let me highlight a few things in Juan's excellent answer, to pave the way a little for a novice. I'll use code extracts, which shows only required things.

Novices shouldn't be intimidated by Tikz' rich syntax, but conquer element by element, similar to the simplifications I use here. Try and buy-in.

## 1. Ellipses

• standalone is a documentclass useful for drawings; replace by article and compile to see the difference
• to define constants he uses TEX notation e.g. \def\h{4}, called by \h later
• I put a help grid to simplify orientation a little
• I increased \h a little to better see the centers
• the % ellipses part is tikz-ish: \draw something , with [options] , (some, where), an ellipse by intention with (parameters) ;
• finally to better see the ellipses's definition I put two \node s with some {text} , and [draw] its shape, i.e. frame

Excerpt from Juans code and extensions:

\documentclass[tikz,border=1.618mm]{standalone}
\usetikzlibrary{backgrounds}

\definecolor{aquamarine}{HTML}{008B9B}

\begin{document}
\begin{tikzpicture}
\def\a{4.5}  % a semiaxis   % TEX-syntax; defines a constant
\def\b{2.25} % b semiaxis
\def\h{3}  % height         % increased separation

% ~~~ for some orientation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\draw [help lines] (-5,-3) grid (5,3);

% ellipses
\begin{scope}[on background layer]
\draw[very thick,red]        (0,0)  ellipse (\a cm and \b cm);
\draw[very thick,aquamarine] (0,\h) ellipse (\a cm and \b cm);

% ~~~ indicating the centers ~~~~~~~~~~~~~~~~~~~~
\node [draw] at (0,0)  {(0/0 - red center)};
\node [draw] at (0,\h) {(0/\h) - green center};
\end{scope}
\end{tikzpicture}
\end{document}


## 2. "Automatic" naming of nodes

Brilliant, and quite a bit to disgest for a novice to Tikz.

• to illustrate I again put a simple help grid, and some text above the following
• \foreach \j in {L,R} will iterate over the set given, here {L,R}, and variable \j will have values L and R while iterating
• the [count=\jj from 0] option introduces a second variable \jj, giving the index or position in said list, i.e. will take the values 0 and 1
• so \node at (\jj,0) {\j}; will be replaced by \node at ( 0 ,0) {L}; during the first loop, and so on
• he reuses this mechanism later to generate names for node positions
• e.g. (RT7) is used to address said node, which was generated beforehand by e.g. (\j T7), when \j had the value R during an iteration

Excerpt from Juans code and extensions:

\documentclass[tikz,border=1.618mm]{standalone}

\begin{document}
\begin{tikzpicture}
% ~~~ help grid, from (0/0) to (1/2), 1 cm each ~~~~~~~
\draw [help lines] (0,0) grid (1,2);
% ~~~ placing a node, with text, draw its shape ~~~~~~~~
\node [draw] at (0,2) {centered text at (0/2)};

% Juan's special, simplified
\foreach[count=\jj from 0]\j in {L,R} % left, right
{
\node at (\jj,0) {\j};
}

% ~~~ just to emphasize placement ~~~~~~~~~~~~~~~~~~~
\draw [dashed,thick] (0,.5) -- (0,1.5);

\end{tikzpicture}
\end{document}


## 3. Other Tikz-syntax

It will be best to download the tikz-manual from ctan, which is also available as an online HTML-version. Let's pick up, what's left to explain or indicate to fully understand Juan's answer.

• tikz-libraries expand Tikz; calc and backgrounds are described in the manual
• \tikzset defines options or attributes for drawings; makes code more readable; example: \node[my node] ... uses the style defined as my node
• \begin{} ... \end{} are environments, defined both in LaTeX and Tikz
• scope is sometimes necessary; see the related chapter
• \node is a Tikz-element you should know by heart, soon; see the related chapter as well as the tutorials in part I
• yshift shifts node content, here along the y-axis; often useful for fine-tuned placements
• $formula$ defines the math environment in LaTeX; as it's text, it can be the content of a node, like \node at (0,0) {$formula$};
• \pgfmathparse and \pgfresult are explained late in the manual: most of the time you can do without, but for the double-circle task it's useful
• Very good!!! (+1). Thanks for the detailed explanations. Commented May 14, 2023 at 9:43
• Thank you: your answer deserves it :) Commented May 14, 2023 at 9:44