Self Complementary Graph Proof

In summary, the problem states that for a graph G that is isomorphic to its complement, with n vertices where n is equal to 4k+1 for some k greater than or equal to 1, the sum of the degrees of the first and last vertex in the degree sequence is equal to n-1, for each value of i from 1 to n. The approach involves finding the number of edges in the graph and working with the degree sequence to prove this statement. The attempt at a solution involves trying to find a contradiction, but further guidance is needed.
  • #1
Trentonx
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Homework Statement


Suppose [itex]G \cong\bar{G}[/itex] and that [itex]n = |V(G)|=4k+1[/itex] for some [itex]k \ge 1[/itex]. Suppose that the degree sequence of G is [itex]d_{1}\ge d_{2} \ge ... \ge d_{n} [/itex]

Prove that [itex]d_{i}+d_{n-i+1}=n-1[/itex] for each [itex]i=1, 2,...,n[/itex]


Homework Equations


I don't think there are any.


The Attempt at a Solution


I put the question in terms of k [itex]d_{i}+d_{4k-i+2}=n-1[/itex]
and found the number of edges, since the graph has to have exactly half the maximum.
[itex]|E(G)| = \frac{n(n-1)}{4}=\frac{(4k+1)(4k)}{4}=4k^{2}+4 [/itex]
I'm not sure that help's, but I thought it might be useful. I need something about the degree sequence, and how it will look, but I'm not sure where to get that.
 
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  • #2
I tried to work out the degree sequence and did a proof by contradiction, but that didn't get me anywhere. Any help is appreciated.
 

FAQ: Self Complementary Graph Proof

What is a self-complementary graph?

A self-complementary graph is a graph in which every vertex is connected to exactly one other vertex. This means that the graph is isomorphic to its own complement.

How do you prove that a graph is self-complementary?

To prove that a graph is self-complementary, you can use the definition of self-complementary graphs and show that every vertex is connected to exactly one other vertex. Another method is to use the concept of graph isomorphism and show that the graph is isomorphic to its own complement.

What is the significance of self-complementary graphs?

Self-complementary graphs have many interesting properties and are often used in mathematical proofs and constructions. They also have applications in coding theory and cryptography.

Can all graphs be self-complementary?

No, not all graphs can be self-complementary. A graph must have an even number of vertices in order to be self-complementary, as each vertex needs to be connected to exactly one other vertex.

How are self-complementary graphs related to other types of graphs?

Self-complementary graphs are a special case of regular graphs, in which every vertex has the same degree. They are also a type of symmetric graph, as they have a symmetry that maps the graph onto itself.

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