Putting nodes tightly next to each other in tikz

Question

I would like to have a shape in my diagram looking like this:

My main problem is to arrange the nodes as tightly as possible. My current approach is

\documentclass{standalone}

\usepackage{tikz}
\usepackage{amssymb}

\begin{document}
\tikzstyle{state}=[circle, draw, minimum size=5mm,inner sep=0pt]
\tikz{
\node[state] (a) {};
\node[left of=a] {$\vartriangleright$};
}
\end{document}

which results in

This is of course not preferable. I just need to know how to place the triangle node as tightly as possible right next to the circle node.

Answer 1

Maybe you want to try this:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \draw [line join=round] (-1,0) -- ++(150:1) -- ++(270:1) -- cycle;
    \draw (0,0) circle (1);
\end{tikzpicture}
\end{document}

I assumed that you use the \vartriangleright command just to get a triangle and not because you need exactly this specific type of triangle. Therefore I have drawn the triangle myself as it is way easier to align then.

As the position of the outer boundary of the circle on the x axis is just the x coordinate of the circle's center minus the radius of the circle, I took this point ((-1,0)) as the reference point for the tip of the triangle. From this point on the triangle is drawn with polar vectors ((<angle>:>length>)) - for a equilateral triangle this is the simplest way as you don't have to calculate the corners in Cartesian coordinates but just give the lengths and angles to the next corner.

Answer 2

The node positioning supports the key node distance. By adjusting the node distance by hand you can move the triangle so that both touch each other.

If you use a TikZ triangle instead of the math character there are other ways to adjust the distance but this works here nicely:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{amssymb}

\begin{document}
\tikzstyle{state}=[circle, draw, minimum size=5mm,inner sep=0pt]
\tikz{
\node[state] (a) {};
\node[left of=a,node distance=10pt] {$\vartriangleright$};
}
\end{document}

and results in: