2 3 1 1 1 0 0 0 0 1 1 1 2 3 1 2 3 1 3 2 2 3 Adjacency matrix Adjacency list

Graphs and Digraphs: A graph G = (V,E) is a structure that represents a discrete set V objects, called vertices or nodes, and a set of pairwise relations E between these objects, called edges. Edges may be directed from one vertex to another or may be undirected. The term “graph” means an undirected graph, and directed graphs are often called digraphs (see Fig. 1). Graphs and digraphs provide a flexible mathematical model for numerous application problems involving binary relationships between a discrete collection of object. Examples of graph applications include communication and transportation networks, social networks, logic circuits, surface meshes used for shape description in computer-aided design and geographic information systems, precedence constraints in scheduling systems.