# Maximum size of G

• January 6th 2012, 04:16 AM
alexmahone
Maximum size of G
Let $G$ be a graph of order $n$ that is not connected. What is the maximum size of $G$?
• January 6th 2012, 04:41 AM
Plato
Re: Maximum size of G
Quote:

Originally Posted by alexmahone
Let $G$ be a graph of order $n$ that is not connected. What is the maximum size of $G$?

What is meant by "the size of G"?
• January 6th 2012, 04:43 AM
alexmahone
Re: Maximum size of G
Quote:

Originally Posted by Plato
What is meant by "the size of G"?

the number of edges in G
• January 6th 2012, 05:38 AM
Plato
Re: Maximum size of G
Quote:

Originally Posted by alexmahone
the number of edges in G

Here is a classic problem.
If $\|\mathcal{E}\|$ is the number of edges and $\|\mathcal{E}\|>\frac{(n-1)(n-2)}{2}$ prove the graph is connected.
• January 6th 2012, 05:48 AM
alexmahone
Re: Maximum size of G
Quote:

Originally Posted by Plato
Here is a classic problem.
If $\|\mathcal{E}\|$ is the number of edges and $\|\mathcal{E}\|>\frac{(n-1)(n-2)}{2}$ prove the graph is connected.

The maximum number of edges in a graph of order $n-1$ is $\binom{n-1}{2}=\frac{(n-1)(n-2)}{2}$. If we add another vertex, any new edge will have to join the new vertex to one of the original $n-1$ vertices and the graph becomes connected.

So, are you saying that the answer to my question in post #1 is $\binom{n-1}{2}$?