# Making a complete graph with one edge in diffrent color

Hi guys I have a problem creating a graph in latex and I will appreciate some help. I want this picture but with the edge between 1 and 4 in thick red. Also If I can somehow have the vertices named and display their names that will be very helpful. I really appreciate input thank you!!!

\begin{tikzpicture}[transform shape]
\foreach \x in {1,...,4}{%
\pgfmathparse{(\x-1)*360/4}
\node[draw,circle,inner sep=0.15cm] (N-\x) at (\pgfmathresult:1.4cm) {};
}
\foreach \x [count=\xi from 1] in {1,...,3}{%
\foreach \y in {\x,...,4}{%
\path (N-\x) edge[ultra thin,-] (N-\y);
}
}
\end{tikzpicture}


For the red part :

\documentclass{standalone}
\usepackage{tikz}
\usepackage{etoolbox}
\begin{document}
\begin{tikzpicture}[transform shape]
\foreach \x in {1,...,4}{%
\pgfmathparse{(\x-1)*360/4}
\node[draw,circle,inner sep=0.15cm] (N-\x) at (\pgfmathresult:1.4cm) {\x};
}
\foreach \x [count=\xi from 1] in {1,...,3}{%
\foreach \y in {\x,...,4}{%
\ifboolexpr{ test {\ifnumcomp{\x}{=}{1}} and test {\ifnumcomp{\y}{=}{4}} }
{\path (N-\x) edge[ultra thin, draw=red,-] (N-\y);}
{\path (N-\x) edge[ultra thin,-] (N-\y);}
}
}
\end{tikzpicture}
\end{document}


See if the following (simple) solution works for you:

\documentclass[tikz, border=3mm]{standalone}

\begin{document}
\begin{tikzpicture}[transform shape]
\foreach \x in {1,...,4}{
\node[draw,circle,inner sep=0.15cm] (N\x) at ({(\x-1)*90}:1.4cm) {};
}
\foreach \x in {1,...,3}{%
\foreach \y in {\x,...,4}{%
\ifnum\x=3
\path (N\x) edge[draw=red,ultra thin] (N\y);
\else
\path (N\x) edge[ultra thin] (N\y);
\fi
}
}
\end{tikzpicture}
\end{document}


• The highlighted edge is between 3 and 4, not 1 and 4 here? – jak123 Mar 16 '16 at 9:37
• @jak123, you have right. I rotate picture for 90 degrees. It is corrected now. However, this doesn't change the showed way how to highlight desired path. – Zarko Mar 16 '16 at 10:14