Sunday 14 August 2011

Graph Theory Definitions


Graph: A set of nodes joined by arcs

Nodes: Points (vertices)

Arcs: Lines (edges)

Simple Graph: A graph without loops or multiple arcs

Subgraph of G: A graph whose nodes and arcs are all in the graph G

Complete Graph, Kn: A simple graph in which each of the nodes is connected by precisely one arc to every other node

Bipartite Graph: These graphs have two sets of nodes. The arcs only connect nodes from one set to the other, and do not connect nodes within a set

Complete Bipartite Graph: Every node in one set is connected to every node in the other set

Trail (Route): A sequence of arcs such that the end node of one arc is the start node of the next

Path: A trail with the restriction that no node is passed through more than once

Cycle: A closed trail where only the initial and final nodes are the same

Order of a Node: The number of arcs meeting at that node

Connected Graph: A graph where, for any two nodes, a path can be found connecting the two nodes

Eulerian Graph: A connected graph which has a closed trail containing every arc precisely once and all nodes 
have even order












Semi-Eulerian Graph: A connected graph with a trail which is not closed that contains every arc precisely once and only 2 nodes have odd order













Non-Eulerian Graph













Planar Graph: A graph which can be drawn in a plane in such a way that arcs only meet at nodes

Euler’s Relationship: For any connected graph drawn in the plane with R regions, N nodes and A arcs, R + N = A + 2

Network (Weighted Graph): A graph whose arcs have weights (numbers)

Digraph (Directed Graph): A graph with directed arcs

Matrix: A table showing all the information about the weights in a network

Tree: A connected graph with no cycles

Spanning Tree: Subgraphs that are also trees

Minimum Spanning Tree: A spanning tree where the total weight of the arcs is as small as possible

©2011 Grant Dwyer

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