Mathematical model in which a set of objects, represented by points called vertices, are connected to one another by links, represented by lines or dashes called arcs or edges. The vertices are labelled.
A graph is therefore made up of two sets: on the one hand, set E of the edges and on the other hand, set V of the vertices. The set of vertices is simply a collection of labels that allow us to distinguish one vertex from another. In an undirected graph, the set of edges is made up of unordered pairs of vertex labels. In a directed graph, the set of arcs is made up of pairs of vertex labels.
Example
Here is a graph G:
Undirected, graph G can be defined by the number V of vertices and the number E of edges:
G = (V, E) where V = {A, B, C, D, E, F} and E = {a, b, c, d, e}.