TikZ Automata Make An Arrow To Nowhere

Question

I have the following TikZ code:

\documentclass{standalone} 
\usepackage{tikz}
\usetikzlibrary{arrows,automata} 
\begin{document}
    \begin{tikzpicture}[shorten >=1pt,node distance=2cm,>=stealth',thick]
        \node[state] (1) {$1$};
        \node[state,draw=none] (d1) [left of=1] {};
        \draw [->] (1) to[loop above] node[auto] {} (1);
        \draw [->] (1) to[bend left] node[auto] {} (d1);
    \end{tikzpicture}
\end{document}

which produces this image:

Notice, that I've used a hidden node (d1) above in order to produce the nice arrow going to the left.

The sadness of this is that now I have a big circle-sized empty space.

I'd like to keep the arrow, I'd like the arrow to look the same, but I'd like to get rid of that empty space.

Is there a way to draw the arrow without introducing the invisible node? Or is there a way to crop the figure? What's an elegant way to solve this problem?

Thanks!

Answer 1

You can use a \coordinate instead of a \node:

\documentclass{standalone} 
\usepackage{tikz}
\usetikzlibrary{arrows,automata} 
\begin{document}
    \begin{tikzpicture}[shorten >=1pt,node distance=2cm,>=stealth',thick]
        \node[state] (1) {$1$};
        \coordinate[left of=1] (d1);
        \draw [->] (1) to[loop above] node[auto] {} (1);
        \draw [->] (1) to[bend left] node[auto] {} (d1);
    \end{tikzpicture}
\end{document}

To compensate for the arrow tip shortening, you could use

   \draw [->,shorten >=0pt] (1) to[bend left] node[auto] {} (d1);

in the above code.

Answer 2

You could also use the ++ option to specify go left 2 centimeters from the last position :

\documentclass{standalone} 
\usepackage{tikz}
\usetikzlibrary{arrows,automata} 
\begin{document}
    \begin{tikzpicture}[thick]
        \node[state] (1) {$1$};
        \draw [->] (1) to[loop above] node[auto] {} (1);
        \draw [->] (1) to[bend left] node[auto] {} ++ (-2,0);
    \end{tikzpicture}
\end{document}

Answer 3

A compact code is

\documentclass{standalone} 
\usepackage{tikz}
\usetikzlibrary{arrows,automata} 
\begin{document}
    \begin{tikzpicture}[thick]
        \node[state] (1) {$1$};
        \draw [->] (1) edge   [loop above]  ()
                       edge   [bend left]   ++ (-2,0);
    \end{tikzpicture}
\end{document}

Answer 4

The actual problem here is, that the invisible node (draw=none) is only used to place the arrow as if there is an actual node. Which works fine but also expands the bounding box.

But there is the special pgfinterruptboundingbox environment. From the PGF manual, 69.3.2 “Graphic Scope Environments”, p. 568f.:

This environment temporarily interrupts the computation of the bounding box and sets up a new bounding box. At the beginning of the environment the old bounding box is saved and an empty bounding box is installed. After the environment the original bounding box is reinstalled as if nothing has happened.

---

To quote from the question:

I'd like to keep the arrow,

Check.

I'd like the arrow to look the same, but I'd like to get rid of that empty space.

Double-check.

Is there a way to draw the arrow without introducing the invisible node?

Yes, see the other answers.

Or is there a way to crop the figure?

Yes, there is an additional way: the \clip (\path[clip]) command/path operation, but that has two disadvantages:

1. It clips only following material.
2. It needs specifying a path that is to be clipped.

What's an elegant way to solve this problem?

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows,automata}
\begin{document}
    \begin{tikzpicture}[shorten >=1pt,node distance=2cm,>=stealth',thick]
        \node[state] (1) {$1$};
        \begin{pgfinterruptboundingbox}
            \node[state,draw=none] (d1) [left of=1] {};
        \end{pgfinterruptboundingbox}
        \draw [->] (1) to[loop above] node[auto] {} (1);
        \draw [->] (1) to[bend left]  node[auto] {} (d1);
    \end{tikzpicture}
\end{document}

Output

(Note, that the arrow is shorten by 1pt and the resulting .png has an additional border of 2pt, hence the arrow does not touch the picture’s margin.)

with draw=none

without draw=none

Answer 5

In the case of your MWE, a simple solution uses the overlay option:

\documentclass{standalone} 
\usepackage{tikz}
\usetikzlibrary{arrows,automata} 
\begin{document}
    \begin{tikzpicture}[shorten >=1pt,node distance=2cm,>=stealth',thick]
        \node[state] (1) {$1$};
        \node[state,draw=none,overlay] (d1) [left of=1] {};
        \draw [->] (1) to[loop above] node[auto] {} (1);
        \draw [->] (1) to[bend left] node[auto] {} (d1);
    \end{tikzpicture}
\end{document}