Tuesday, September 7, 2010

Introduction of Graphs


A graph consists of two sets V and E.
  • V is finite and non empty set of vertices
  • E is a set of edges connecting two vertices. 

Graphs can be directed or undirected

Directed Graph: If all the edges of a graph have specific direction then this type of graph is called directed graph.For Example: V = {1,2,3,4} and E={(1,2), (2,3), (2,4), (3,1), (4,1), (4,3)}Then Directed Graph G={V,E} represented as


    Undirected Graph: If all the edges of the graphs has no specific direction then this type of graph  is known as undirected graph.For Example: V = {1,2,3,4} and E={(1,2), (1,3),(1,4), (2,1),(2,3),(2,4), (3,1),(3,2),(3,4), (4,1),(4,2), (4,3)}Then Undirected Graph G={V,E} represented as



     Representation of Graph

    Adjacency Matrix: It is the two dimensional array or matrix representation of graph. In the matrix, the element a(i,j)= 0 if there is no edge between vertex i and j; the element a(i,j)=1 if there is an edge between vertex i and j. It is also known as Static Representation of graph.

    For Example : Consider the following Directed Graph.  The Adjacent Matrix is 
            1    2     3     4
    1      0    1     0     0
    2      0    0     0     1
    3      0    0     0     0
    4      1    0     1     0




    Consider the following Undirected Graph.  The Adjacent Matrix is  


            1    2     3     4
    1      0    1     0     1
    2      1    0     0     1
    3      0    0     0     0
    4      1    1     1     0

    Adjacency List: It is the list representation of graphs. In this representation, if there are n vertices then there are n linked list for each vertex of graph. It is also known as Dynamic Representation of graph.

      Traversing a Graphs

      Exploring each vertex of the graph is known as traversing a graph. The order in which we explored the vertices depend upon what kind of data structure is used.  The two common graph traversal method are
      1. Breadth First Search (BFS)
      2. Depth First Search (DFS)

      Spanning Tree 
      A tree T is a spanning tree of a graph G={V,E} if every vertex of G belongs to an edge in T and theedges in T form a tree. Details...

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