% This is a TikZ implementation of the extended Dynkin diagram for the class E6.
% The numbering follows the one used by LiE (http://http://wwwmathlabo.univ-poitiers.fr/~maavl/LiE/).
% The highest root is denoted by \star or \gamma_{\star} and has a different colour.
%
%  You'll need to load the following packages
%% \usepackage{tikz}
%% \usetikzlibrary{calc}   % this is needed in order to be able to do coordinate calculations
%% \usetikzlibrary{topaths}
%% \usetikzlibrary{decorations}
%% \usetikzlibrary{decorations.pathmorphing}
%
% Feel free to use it whereever you like, but please leave my name in the drawing.
% 
% 08/04/2015, P. Meessen 
\begin{center}
   \begin{tikzpicture}[scale=.7]
    %%%%%%%%    08/04/2015, P. Meessen 
    %% draw the background coordinate-grid, clearly not needed when finished
    %\draw[step=.5cm,color=gray] (0,0) node[anchor=north east] {$(0,0)$} grid (15,5) node[anchor=south west] {$(15,5)$};
    %% Draw the part for the highest root
    \draw[color=green!51!blue, line width=1pt, dashed] (9,4) -- (9,6);
    \fill[green!51!blue] (9,6) circle (7pt) node[anchor=east] {$\star$~~};
    %% Draw the horizontal roots
    \foreach \x in {1,...,5}{
      \pgfmathparse{ 2*\x +3 };
      \pgfmathresult;
      \let\y\pgfmathresult;
      \fill[black] (\y , 2) circle (7pt) node[anchor=north] {};
    }
    %% Draw the lines connecting the horizontal roots
   \draw[color=black, line width=1pt] (5,2) -- (13,2);
   %% Draw the vertical root
   \draw[color=black, line width=1pt] (9,2) -- (9,4);
   \fill[black] (9,4) circle (7pt) node[anchor =east] {$2$~~};
   %% Write the labeling
   \draw  (5,1.4) node[color= black] {$1$};
   \foreach \x in {3,...,6}{
      \pgfmathparse{ 2*\x +1 };
      \pgfmathresult;
      \let\y\pgfmathresult;
      \draw  (\y,1.4) node[color= black] {$\x$};
    }
   %% Indicate that this Dynkin diagram is for e_7
   \draw (6,4) node[color=black] {$\mathfrak{e}_{6}$};
   \end{tikzpicture}
\end{center}