Number of Complete Bipartite Graphs with n Vertices

In summary, the question is asking how many complete bipartite graphs can be formed with n vertices. To answer this, we can let the first bipartition set have x vertices and the second bipartition set have y vertices, with x+y=n. Then, the formula C(n, x)*C(n-x, y)=C(n,x)*C(y,y)=C(n,x) can be used to calculate the number of complete bipartite graphs with the "first" partition having size x. The possible values for x are n, so the answer would be n*C(n,x). However, it should be noted that x was arbitrarily chosen and may not necessarily be the optimal value. Another approach could be using the formula C
  • #1
schaefera
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0

Homework Statement


How many complete bipartite graphs have n vertices?


Homework Equations





The Attempt at a Solution


I said, let the first bipartition set have x vertices and the second bipartition set have y vertices. So x+y=n.

I think that you would do C(n, x)*C(n-x, y)=C(n,x)*C(y,y)=C(n,x) but I feel like this is either wrong or not good since I made x and y up arbitrarily.

Help?
 
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  • #2
So that's the number of complete bipartite graphs with the "first" partition having size x. What are the possible values for x?
 
  • #3
There are n possible values for x... so is the answer n*C(n,x)?

Is there any problem with me having made x up without it being in the problem?

Also, would I instead want to do something like C(x,1)*C(y,1) [to get the number of ways to pick the vertices] *C(n,x) [to get the number of ways of making the 'first' bipartition set] *n?
 
  • #4
Could it matter if there is an even/odd number of vertices in anyone bipartition set?
 
  • #5
Any new ideas?
 

1. What is a complete bipartite graph?

A complete bipartite graph is a type of graph in which the vertices can be divided into two sets, such that every vertex in one set is connected to every vertex in the other set. In other words, there are no edges within each set, only between the two sets. This type of graph is denoted as Kn,m, where n and m represent the number of vertices in each set.

2. How many edges does a complete bipartite graph have?

A complete bipartite graph with n vertices in one set and m vertices in the other set has n x m edges. This is because each vertex in one set is connected to all vertices in the other set, resulting in n x m total connections.

3. What is the degree sequence of a complete bipartite graph?

The degree sequence of a complete bipartite graph is (m, m, ..., m, n, n, ..., n), where there are m vertices with degree n and n vertices with degree m. In other words, the degree sequence alternates between the two sets of vertices.

4. How can complete bipartite graphs be used in real-world applications?

Complete bipartite graphs can be used to model relationships between two distinct groups, such as male and female students in a school or buyers and sellers in a market. They can also be used in scheduling problems, as each set of vertices can represent a different group of tasks or resources.

5. Are complete bipartite graphs planar?

No, complete bipartite graphs are not planar. This is because they contain a subgraph that is isomorphic to K3,3, which is known to be non-planar. In other words, it is impossible to draw a complete bipartite graph on a plane without any edges crossing.

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