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This questions is a follow-up question to Drawing A2xA2 Dynkin diagram with dynkin-diagrams

I edited the above question but not sure if anyone saw that, apologies for duplicating a question.

The questions are

  1. Is there existing code to draw an ellipse around several nodes in a Dynkin diagram?
  2. In folding style can one choose to have the arms straight instead of curved.
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    Kindly have just one question per question ;-)
    – MS-SPO
    Jul 26, 2023 at 11:23

1 Answer 1

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Here seems to be a way to do it: result

To your first question, where I build upon the solution from Sandy G:

  • this package is compatible with Tikz, see intro in manual
  • so for orientation I draw a course (1cm) and a fine (2mm) grid
  • with some trial and error I put an ellipse there
  • see ch. "2.5 Circle Path Construction" in the tikz-manual

The position of the points inside the ellipse seem to depend on the scale chosen, here 0.3cm, and there may be better ways to access these coordinates without guessing.

For the second question I used the example on p. 57 in the dd-manual. On the fly I didn't recognise further options to modify lines. Feel free to contact the author of the package, e.g. via https://ctan.org/pkg/dynkin-diagrams.

\documentclass[12pt]{amsbook}
\usepackage{dynkin-diagrams}

% Adjusting solution from Sandy G, https://tex.stackexchange.com/a/623517/245790

\begin{document}

%Is this:
 \begin{dynkinDiagram}[name=upper]A2
    % ~~~ Where are we? ~~~~~~~~~~~~~~~~~~~~~~
    % ~~~ adding grid for orientation ~~~~~~~~~~~~
    \draw[help lines] (0,0) grid (1,1);
    \draw[gray!20,step=2mm] (0,0) grid (1,1);
    
    % ~~~ What's shown there? ~~~~~~~~~~~~~~~~
    % ~~~ past solution ~~~~~~~~~~~~~~~~~~~~
    \node (current) at ($(upper root 1)+(0,-.3cm)$) {};
    \dynkin[at=(current),name=lower]A2
    % ~~~ dropping the vertical lines ~~~~~~~~~~~~~
        %\begin{pgfonlayer}{Dynkin behind}
        %\foreach \i in {1,2}{%
        %\draw[/Dynkin diagram/fold style] ($(upper root \i)$) -- ($(lower root \i)$);}
        %\end{pgfonlayer}
    
    % ~~~ Who let the ellipses out? ~~~~~~
    % ~~~ with a little trial&error ~~~~~~~~
    \draw[red] (0.35,-0.06) ellipse[x radius=0.15, y radius=.4];
 \end{dynkinDiagram}
%what you want?

% ~~~ About the folds: taken from page 57, ch. "31 Other examples" ~~~~
 \begin{tikzpicture}
    \dynkin[odd,fold]A[2]{oo.oto.oo};% curved
 \end{tikzpicture}
 
 \begin{tikzpicture}
    \dynkin[odd]A[2]{oo.oto.oo};% non-curved, i.e. dropped "fold"
 \end{tikzpicture}

\end{document}

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