Digraph Automorphisms: Counting Edge Colorings

  • Thread starter Monte_Carlo
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In summary, the conversation revolves around a digraph automorphisms problem in abstract algebra. The digraph has four vertices and three edges, and the question asks for the number of ways to color the edges using different colors. The options include only white, both white and blue, all three colors (green, red, and blue), and all red, all blue, or a mix of red and blue. The person asking the question is unsure of the correct answers and is seeking guidance and opinions. They also mention possible mistakes in their post and inquire about the appropriate section to post in.
  • #1
Monte_Carlo
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Hello,

I have the following abstract algebra problem. It has to do with digraph automorphisms.

You're given a digraph G with vertices V(G) = {x, y, z, w} and edges E(G) = { (x, y), (x, z), (x, w) }. How many essentially different ways are there to color the edges of G using the following colors:

1) only white
2) both white and blue, each at least once
3) green, red and blue, each at least once
4) all red, all blue or some red and some blue

For 1), I think the answer is 1
For 2), I think the answer is 2 but it disagrees with the answer in the book.

Please give me some direction and opinion, I don't think just answers will be useful.

Thanks,

Monte
 
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  • #2
Since it's the first time I've posted a request for homework assistance, I realize I might have made several mistakes which would explain why nobody has proffered an attempt at solution. For one, I'm not sure if this section of the forum is the right one. I've seen descriptions of other sections, for example one for abstract algebra. However, there is an instruction not to post homework problems there. The problem I'm asking about is not, strictly speaking, a homework problem, but it is one at the end of a textbook chapter.

I'd be happy to hear if there is any other additional information that would be expected from me to elicit an attempt at solution from anybody at this forum.

Thanks,

Monte
 

1. What is a digraph automorphism?

A digraph automorphism is a permutation of the vertices of a directed graph that preserves the edges. In other words, the automorphism maps each vertex to another vertex and maintains the direction of the edges between them.

2. What is the significance of counting edge colorings in digraph automorphisms?

Counting edge colorings in digraph automorphisms is important because it helps in understanding the structure and symmetry of a directed graph. It also has practical applications in fields such as network theory and coding theory.

3. How do you count edge colorings in digraph automorphisms?

To count edge colorings in digraph automorphisms, one must first determine the number of possible automorphisms for a given directed graph. This can be done by identifying the cycles and fixed points in the graph. Then, the number of distinct colorings for each cycle and fixed point can be calculated using combinatorial techniques.

4. What is the relationship between digraph automorphisms and edge colorings?

The relationship between digraph automorphisms and edge colorings is that the number of edge colorings in a directed graph is equal to the number of distinct automorphisms for that graph. This is known as the Edge Color Automorphism Theorem.

5. How does counting edge colorings in digraph automorphisms contribute to graph theory?

Counting edge colorings in digraph automorphisms is a fundamental concept in graph theory that helps in understanding the symmetry and structure of directed graphs. It also has significant applications in areas such as network theory, coding theory, and cryptography.

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