Graph Theory: Complement of a Graph

In summary, it is possible for a graph G and its complement G' to be complete. This can be seen by starting with a complete graph K_3 and finding its complement, where the missing edges in G would be present in G'. This concept can also be applied to other complete graphs G on n vertices.
  • #1
jack_bauer
10
0
I'm wondering, is it possible a graph G and its complement G' to be complete?
 
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  • #2
Start with the complete graph [tex] K_3 [/tex], and find its complement. What do you notice? Think about the definition of the complement of a graph and think about what would happen in general.
 
  • #3
A complete graph G on n vertices is a graph that has an edge between any two vertices, no matter which two you pick. The complement of G is a graph of n vertices and is constructed by drawing the n vertices on the paper and then filling in the edges that are not present in G. Which edges are missing in G if G is complete?
 
  • #4
jack_bauer said:
I'm wondering, is it possible a graph G and its complement G' to be complete?

Sure, for K_0 and K_1.
 
  • #5
i think you mean G union G' to be complete?
 

FAQ: Graph Theory: Complement of a Graph

What is the complement of a graph?

The complement of a graph is a new graph that contains all the same vertices as the original graph, but the edges are reversed. In other words, if two vertices in the original graph are connected by an edge, they will not be connected in the complement graph, and vice versa.

How is the complement of a graph represented?

The complement of a graph can be represented either as a list of edges or as an adjacency matrix. In both cases, the complement graph will have the same number of vertices as the original graph, but the connections will be reversed.

What is the purpose of finding the complement of a graph?

The complement of a graph is useful in a variety of applications, including network analysis, graph coloring, and circuit design. It can also help identify patterns or relationships within a graph that may not be as easily visible in the original graph.

How is the complement of a graph calculated?

The complement of a graph can be calculated using a simple formula where the number of edges in the complement graph is equal to the number of possible edges minus the number of edges in the original graph. For example, if the original graph has 5 vertices and 8 edges, the complement graph will have 5 vertices and (5*4)/2 - 8 = 2 edges.

Are there any special types of graphs that do not have a complement?

Yes, a self-complementary graph is a graph that is isomorphic to its own complement. In other words, the complement of a self-complementary graph is identical to the original graph. There are also graphs that do not have a complement, such as null graphs (graphs with no edges) and complete graphs (graphs where every pair of vertices is connected by an edge).

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