defining graph notes graph consists of set of vertice (nodesand set of edges (arcswe write =( ,ev is finite and non empty set of vertices is set of pairs of verticesthese pairs are called edges therefore ( )read as of gis set of verticesand ( )read as of gis set of edges an edge ( , )is pair of vertices and wand is said to be incident with and graph may be pictorically represented as given in figure figure graph we have numbered the nodes as , , , and therefore ( ( and ( {( )( )( )( )( )( )( )you may notice that the edge incident with node and node is written as ( , )we could also have written ( , instead of ( , the same applies to all the other edges thereforewe may say that ordering of vertices is not significant here this is true for an undirected graph in an undirected graphpair of vertices representing any edge is unordered thus ( ,wand ( ,vrepresent the same edge in directed graph each edge is an ordered pair of verticesi each edge is represented by directed pair if ( , )then is tail or initial vertex and is head or final vertex subsequently ( ,wand ( ,vrepresent two different edges directed graph may be pictorically represented as given in figure lovely professional university