Graphs and Multigraphs:

A graph represented by G (V,E) consists of two things :
(1) A set V of elements called vertices (or points or nodes)
(2) A set E of edges such that each edge eiE is identified with a unique (unordered) pair [vi , vj] of vertices in V, denoted by ei=[ vi , vj]









The above graph consists of 5 vertices and edges

Suppose ei or ej=[ vi , vj]. Then the vertices vi and vj are called endpoints of e, and vi and vj are said to be adjacent vertices or neighbors. The degree of a vertex v, written deg (v), is the number of edges containing v. If deg(v)=0-that is, if v does not belong to any edge-then v is called an isolated vertex.