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*}.