graphs of relations

Complete

Summary

Undirected graph

  • no arrows, edges are like arrows in both directions
  • symmetric/two-way relations
  • uses sets
abcd

Directed graph

  • with arrows
  • one-way relations
  • uses tuples
abcd(a,c)(c,a)

Extra

Tikz template for directed/undirected graphs

latex
\usepackage{tikz}
\usetikzlibrary{calc}
% https://tex.stackexchange.com/questions/354199/how-to-make-an-arrow-from-a-node-to-itself-have-a-nice-arc
\def\loopsize{6mm}
\newcommand\round[4][-]%
  {
	\draw[#1] ($(#2.#3) + {cos(#3)}*(0, {0.71*(\loopsize/2)}) - {sin(#3)}*({0.71*(\loopsize/2)}, 0)$) arc (180+#3-45:180+#3-45-270:\loopsize/2) #4;
  }
\begin{document}
\begin{tikzpicture}[auto, node distance=2cm]

  \node (a) {a};
  \node (b) [below left of=a] {b};
  \node (c) [below right of=a] {c};
  \node (d) [below of=a] {d};

  \loop[-]{a}{45}
  
  \draw[-] (a) edge (b);

\end{tikzpicture}
\end{document}