How do I change the radius of circle in a node in tikz style?

Question

I have the following example:

\documentclass[]{beamer}
\usetheme{Darmstadt}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
    \begin{frame}{}
        \begin{tikzpicture}[>=latex]
        \tikzstyle{vertex} = [circle, fill=black!10]
        \tikzstyle{selected vertex} = [circle, radius=0.1cm, fill=red!30]
        \tikzstyle{nedge} = [-]

        \node[vertex] (v1) at (3,0) {v1};
        \node[vertex] (v2) at (0,-1) {v2};
        \node[vertex] (v3) at (6,-1) {v3};
        \draw[nedge] (v1) -- (v2);
        \draw[nedge] (v1) -- (v3);
    \end{tikzpicture}
\end{frame}
\end{document}

I want to change the radius of vertice in tikz style. How to do it? Thanks for the help.

Answer 1

First, don't use tikzstyle which is deprecated, but use tikzset instead. Then, define your nodes as circle with inner sep=0pt (you can also set the outer sep to 0pt), and with a minimum width which is your node diameter.

Finally, you can make other node style inherit a previous one like I did. The selected vertex inherits all parameters from the vertex style, and you can add/replace some afterwards (like the filling here).

\documentclass[]{beamer}
\usetheme{Darmstadt}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
    \begin{frame}{}
        \begin{tikzpicture}[>=latex]
        \tikzset
            {
            vertex/.style={circle, inner sep=0pt, outer sep=0pt, minimum width=1cm,fill=black!10},
            selected vertex/.style = {vertex, fill=red!30},
            nedge/.style = {-}
            }

        \node[vertex] (v1) at (3,0) {v1};
        \node[vertex] (v2) at (0,-1) {v2};
        \node[vertex] (v3) at (6,-1) {v3};
        \draw[nedge] (v1) -- (v2);
        \draw[nedge] (v1) -- (v3);
    \end{tikzpicture}
\end{frame}
\end{document}