[Tex/LaTex] How to connect two parents to the same child, with parents not in the same tree

forestnodestikz-pgftikz-trees

I'm trying to draw a specific tree, with two parents node linked to the same child. The problem is that one of the parent is outside the main tree.

Here's the code I have for the moment:

\documentclass{article}
\usepackage{tikz-qtree,tikz-qtree-compat}
%\usepackage{gb4e}
\usepackage{forest}

\begin{document}

%\begin{exe}
\begin{forest}
qtree edges/.style={for tree= parent anchor=north, child anchor=south}
   [A, grow=north
       [C, name=C, grow'=north
           [D, grow=north ]
           [E, name=t5, grow=north ]
       ]
       [B, grow=north ]
   ]
   \hspace{0.8cm}
   [$F$, name=F, grow=north ]
   %\draw (F.north) -- (C.south);
\end{forest}
%\end{exe}

\end{document}

I'd like the nodes F and C to be connected. I don't know why, but if I delete the dollar signs, node F doesn't even appear on my document.

Another thing is that I want the forest environment to be embedded in an example environment, but this doesn't work either.

Thanks in advance for your help!

Best Answer

There are various problems with your code. First, multirooted structures are not formally trees, so you can't expect tree drawing packages to handle them directly. See the following question for more discussion on techniques for this:

Multi-rooted Tree-like Structures and Nodes with Multiple Parents in LaTeX

Furthermore, the syntax for a gb4e example requires that the example be introduced by the \ex macro (within the {exe} environment.)

To handle the multidominance, I've used Ignasi's suggestion to create a node relative to the -| path between node A and E. You could also use the TikZ positioning library, to manually place the node. I've also removed the tikz-qtree package, since it's not needed if you're using forest. Since your 'tree' grows upwards, I've added baseline to one of the terminal nodes so that it will align properly with the example number, and set the growth function globally for the tree. Also, you had a particular style for nodes in your example, but you never applied that style, and I've done that too.

You should also load gb4e after most other packages, since it can cause problems otherwise.)

\documentclass{article}
\usepackage{forest}

\usepackage{gb4e}


\begin{document}

\begin{exe}
\ex
\begin{forest}
qtree edges/.style={for tree={parent anchor=north, child anchor=south}},
for tree={grow=north},qtree edges
   [A, name=A,
       [C, name=C 
           [E,baseline,name=E  ]
           [D,   ]
       ]
       [B ]
   ] 
   \node  (F) at (A-|E) {F};
   \draw (F.north) -- (C.south);
   \end{forest}
\end{exe}

\end{document}

output of code

Related Solutions

[Tex/LaTex] Drawing a tree where many nodes have the same child in TikZ

You can use two trees sitting on top of each other.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[sibling distance=2.5cm]
\node (topnode) at (0,5) { {\{\{1\}\{2\}\}\{3\}\{4\}}\} } 
child { node {{\{\{1,2\}\{3\}\{4\}}\}} }
child { node {{\{\{1,3\}\{2\}\{4\}}\}} }
child { node {{\{\{1,4\}\{2\}\{3\}}\}} }
child { node {{\{\{2,3\}\{1\}\{4\}}\}} }
child { node {{\{\{2,4\}\{1\}\{3\}}\}} }
child { node {{\{\{3,4\}\{1\}\{2\}}\}} }
;

\node[minimum width=3cm](bottomnode) {\{\{1,2,3,4\}\}} [grow'=up]
child { node {{\{\{1,2,3\}\{4\}}\}} }
child { node {{\{\{1,2,4\}\{3\}}\}} }
child { node {{\{\{1,2\}\{3,4\}}\}} }
child { node {{\{\{1,3,4\}\{2\}}\}} }
child { node {{\{\{1,3\}\{2,4\}}\}} }
child { node {{\{\{1,4\}\{2,3\}}\}} }
child { node {{\{\{2,3,4\}\{1\}}\}} }
;
\foreach \x in {1,2,3}{
\draw (topnode-1) -- (bottomnode-\x);
}
\end{tikzpicture}
\end{document}

enter image description here

I'll leave the connection lines to you if you don't mind. You can access each node by first writing up the parent node name followed by a dash and the item number e.g. (topnode-5).

[Tex/LaTex] Changing the indentation of a Tikz tree

Let's provide a different example which shows better your problem:

% Assumming preamble as provided in the question
    \tikzset{
    dirtree/.style={
      growth function=\dirtree@growth,
      every node/.style={anchor=north},
      every child node/.style={anchor=west},
      edge from parent path={(\tikzparentnode\tikzparentanchor) |- (\tikzchildnode\tikzchildanchor)}
  }
}
\makeatother
\begin{document}
\begin{tikzpicture}[dirtree]
\node {toplevel} 
    child { node {Foobarish}
            child { node  {foobar} 
                    child { node {foo}} 
                  }
            child { node  {foo} 
                    child {node {foo} } 
                  }
            child { node  {bar} }
    }
    child { node {Bar}
        child { node {foo} }
        child { node {foo} }
    };
\end{tikzpicture}

The output is:

Output

This shows not only the issue you mention, but also that the vertical stems in each branch are not aligned (the branch from Foobarish is not aligned with the branch from Bar). This problem will be also solved with a proper parent anchor (and growth parent anchor) which does not depend on the size of the parent. In this case south west is the best choice.

The following style solves all these issues, and provides a very compact version of the tree.

\tikzset{
  dirtree/.style={
    growth function=\dirtree@growth,
    growth parent anchor=south west,
    parent anchor=south west,
    every child node/.style={anchor=west},
    edge from parent path={([xshift=2ex] \tikzparentnode\tikzparentanchor) 
                           |- (\tikzchildnode\tikzchildanchor)}
  }
}

Final result

Thanks to Andrew Stacey and Jake for their useful comments about the need to set also growth parent anchor (their comments below refer to an early version of this answer).

Best Answer

Related Solutions

[Tex/LaTex] Drawing a tree where many nodes have the same child in TikZ

[Tex/LaTex] Changing the indentation of a Tikz tree

Related Question