 Theta graph

The theta graph ${\Theta }_n$ has two vertices joined by $n$ edges. It has first Betti number $n-1$ and occurs as the link of a point on the spine of a book with $n$ two-dimensional pages.

A theta graph is a type of graph used in the study of graph theory, particularly in the context of network flow problems and duality in optimization. Specifically, a theta graph is a form of representation that consists of two terminal vertices (often denoted as \( s \) and \( t \)), two or more paths connecting these vertices, and possibly some additional vertices that act as intermediate points along the paths.