# some arrows do not appear

The following code produces two graphs and I wanted arrows everywhere, but only some edges are arrows, the other are normal edges.

I don't understand how it is even possible. The arrow edges in the end are p1->p2, q2->q3 and q2'->q4

\begin{tikzpicture}
\tikzstyle{vertex}=[draw,circle]
\node at (-1,-.5) {$H:$};
\node[vertex] (p1) at (0,0) {};
\node[vertex] (p2) at (0,-1) {};
\node[vertex] (p3) at (-1,-2) {};
\node[vertex] (p4) at (1,-2) {};
\draw[->] (p1) -- (p2);;
\draw[->] (p2) -- (p3);
\draw[->] (p2) -- (p4);
\node at (3.5,-.5) {$G:$};
\node[vertex] (q1) at (5,0) {};
\node[vertex] (q2) at (4,-1) {};
\node[vertex] (q2') at (6,-1) {};
\node[vertex] (q3) at (4,-2) {};
\node[vertex] (q4) at (6,-2) {};
\draw[->] (q1) -- (q2);
\draw[->] (q1) -- (q2');
\draw[->] (q2) -- (q3);
\draw[->] (q2') -- (q4);
\end{tikzpicture}

• Welcome! Thanks for providing code. If you could complete it to make it compilable, that would be great. – cfr Feb 15 '16 at 23:42
• Your code produces 2 graphs here: the 1st contains 3 arrows; the 2nd contains 4. – Sigur Feb 15 '16 at 23:42
• I get arrows everywhere, too, when I just add minimal code needed to compile. [Though this is a very inefficient way to draw trees.] – cfr Feb 15 '16 at 23:43
• Maybe it is a zoom problem. – Sigur Feb 15 '16 at 23:45
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TikZ has a graph drawing library which will make the drawing of these graphs significantly easier.

In the following example, the baseline key sets the vertical alignment of the graphs with the H and G. With each node, the part before the slash / identifies the node uniquely so that it can be used again in the layout specification. For example, you cold add another edge connecting nodes 3 and 4 in H by adding 3 -- 4, in the graph specification.

The part in the quotes determines the label (or text) in the node.

\documentclass[convert]{standalone}

\usepackage{tikz}
\usetikzlibrary{
graphs,
graphdrawing,
}
\usegdlibrary{trees}

\begin{document}
$$H$$:
\tikz [baseline=(2), >=stealth] \graph [tree layout, nodes={draw,circle}] {
1/"" -> 2/"" -> {3/"", 4/""},
};
$$G$$:
\tikz [baseline=(2), >=stealth] \graph [tree layout, nodes={draw,circle}] {
1/"" -> {2/"" -> 3/"", 4/"" -> 5/""},
};
\end{document}