Determining if this degree sequence is graphic

In summary, the conversation discusses determining if a given degree sequence is graphic using the Havel-Hakimi theorem. The steps for applying the theorem are mentioned, including checking for an even sum and reordering the sequence from largest to smallest after subtracting 1 from the next element. It is noted that the sequence provided is not graphic due to a mistake in applying the algorithm, but with the correct steps, it is shown to be graphic.
  • #1
in the rye
83
6

Homework Statement


Determine if the degree sequence 3,3,2,2,2,2 is graphic.

Homework Equations


Havel-Hakimi

The Attempt at a Solution


[/B]

Check to see if the sum is even:
3+3+2+2+2+2 = 16It is even, therefore apply Havel-Hakimi

3,3,2,2,2,2 -> remove the 3 and subtract the next 3 by 1
2,1,1,2,2 -> remove the 2 and subtract the next 2 by 1
0,0,2,2 -> reorder from largest to smallest
2,2,0,0 -> remove the 2 and subtract 1 from the next 2
1,-1,0 -> reached a negative, stop

Therefore the sequence is not graphic.

The solution says it is graphic and provides no explanation.

Am I misunderstanding Havel-Hakimi Theorem?
 
Last edited:
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  • #2
Maybe I don't understand your steps. It looks to me like you did not reorder every time it was necessary to make the sequence non-increasing.
 
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  • #3
FactChecker said:
Maybe I don't understand your steps. It looks to me like you did not reorder every time it was necessary to make the sequence non-increasing.
Facepalm. I completely missed that... I went back an re-looked at the problem before coming back to this post. It worked out when I applied the alogorithm correctly... thanks haha
 
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Related to Determining if this degree sequence is graphic

1. What is a degree sequence?

A degree sequence is a list of numbers representing the degrees of each vertex in a graph.

2. How can I determine if a degree sequence is graphic?

A degree sequence is graphic if it can be represented by a simple graph with the given degrees for each vertex.

3. What is a simple graph?

A simple graph is an undirected graph with no loops or multiple edges between any two vertices.

4. What is the Havel-Hakimi algorithm?

The Havel-Hakimi algorithm is an algorithm used to determine if a given degree sequence is graphic by repeatedly removing the largest degree and decreasing the remaining degrees until either a graphic sequence is obtained or it is proven to be non-graphic.

5. Can a non-graphic degree sequence be made graphic by rearranging the numbers?

No, a non-graphic degree sequence cannot be made graphic by rearranging the numbers. The Havel-Hakimi algorithm shows that if a degree sequence is non-graphic, it cannot be made graphic by rearranging the numbers.

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