What is "graph"

To graph theory is a branch of mathematics that studies the relationships between the objects of a given set. For this are employed structures called graphs, G(V,A), where V is a nonempty set of objects called vertices and A is a set of unordered pairs of V, called edges.

Depending on the application, edges may or may not have direction, it may be permissible whether or not edges bind a vertex to itself and vertices and/or edges may have an associated (numerical) weight. If the edges have an associated direction (indicated by an arrow in the graphic representation) we have a directed graph, oriented graph or digraph. A graph with a single vertex and no edges is known as the trivial graph.

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