# Preserving the rooted tree layout in graphs

I am working in a research project where I deal with rooted trees. I want to be able to add edges to the rooted tree and somehow "preserve" the rooted tree layout. More precisely, if I add the edges $(2,8)$ and $(3,6)$ in the rooted tree produced by the code below

G=Graph({0:[1,2,3,4],1:[5,6,7],4:[8,9,10],6:[11,12],9:[13,14]})
G.show(layout='tree',tree_root=0)
G.show()


the layout of the updated graph is kind of messy and it gets worse if the order of the tree is increased. I want to add the new edges in a different color but without affecting the layout of the initial tree. I want the updated graph to look like the output of this tikzpicture:

  \begin{tikzpicture}[
V/.style = {% V as Vortex
circle,thick,fill=orange},scale=0.4]

%drawing nodes
\node[V] (0) at (-9,11) [scale=0.5,draw] {0};
\node[V] (1) at (-3,8) [scale=0.5,draw] {1};
\node[V] (2) at (-7,8) [scale=0.5,draw] {2};
\node[V] (3) at (-11,8)[scale=0.5,,draw] {3};
\node[V] (4) at (-15,8) [scale=0.5,draw] {4};
\node[V] (5) at (-1,5) [scale=0.5,draw] {5};
\node[V] (6) at (-3,5) [scale=0.5,draw] {6};
\node[V] (7) at (-5,5) [scale=0.5,draw] {7};
\node[V] (8) at (-13,5) [scale=0.5,draw] {8};
\node[V] (9) at (-15,5) [scale=0.5,draw] {9};
\node[V] (10) at (-17,5) [scale=0.4,draw] {10};
\node[V] (11) at (-2,2) [scale=0.4,draw] {11};
\node[V] (12) at (-4,2) [scale=0.4,draw] {12};
\node[V] (13) at (-14,2) [scale=0.4,draw] {13};
\node[V] (14) at (-16,2) [scale=0.4,draw] {14};

\draw[black,very thick]
(0) to (1)
(0) to (2)
(0) to (3)
(0) to (4)
(1) to (5)
(1) to (6)
(1) to (7)
(6) to (11)
(6) to (12)
(4) to (8)
(4) to (9)
(4) to (10)
(9) to (13)
(9) to (14);

\draw[green,very thick,dotted]
(3) to (9)
(2) to (6);
\end{tikzpicture}


Is this even possible?

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You can save the positions of the vertices as follows:

sage: G.show(layout='tree',tree_root=0, save_pos=True)


Then, when you add edges, the "optimal" position of the vertices is not recomputed.

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Thank you! Unfortunately I do not have enough reputation to upvote this answer.

( 2018-07-22 12:49:07 -0600 )edit

If you post anonymously or as a wiki, then you can not get karma, hence you can not get rights.

( 2018-07-22 16:28:53 -0600 )edit