Maximum Degree of Subgraphs

Oct 13, 2025 by wbrum.org 137 views

Introduction

In graph theory, a multigraph is a graph that allows multiple edges between any two vertices. This concept is an extension of the traditional graph theory, where each edge is unique and distinct. The maximum degree of a multigraph, denoted by $\Delta(G)$ , is the largest number of edges incident on any vertex. In this article, we will explore the problem of decomposing a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees.

Problem Statement

Let $\Delta(G)$ denote the maximum degree of a multigraph $G$ (with no loops). We are interested in finding examples of multigraphs $G$ (with no loops) with the following property: For any nonempty proper subgraph $H$ of $G$ , the sum of the maximum degrees of $H$ and $G-H$ is at least $\Delta(G)$ . In other words, we want to decompose the multigraph $G$ into two subgraphs $H$ and $G-H$ such that the sum of their maximum degrees is at least $\Delta(G)$ .

Motivation

The problem of decomposing a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees has several motivations. Firstly, it is a natural extension of the traditional graph decomposition problem, where the condition is typically on the number of edges or vertices. Secondly, it has applications in network design, where we want to partition a network into two subnetworks with specific properties. Finally, it is a challenging problem that requires a deep understanding of graph theory and its various concepts.

Approach

To tackle this problem, we will employ a combination of graph theoretical techniques and computational methods. We will start by analyzing the properties of multigraphs and their subgraphs. We will then use graph algorithms to find examples of multigraphs that satisfy the given condition. Finally, we will use computational methods to verify the results and explore the properties of these examples.

Properties of Multigraphs

A multigraph $G$ is a graph that allows multiple edges between any two vertices. This means that each edge is a pair of vertices, and there can be multiple pairs of vertices with the same edge. The maximum degree of a multigraph $G$ , denoted by $\Delta(G)$ , is the largest number of edges incident on any vertex. In other words, it is the largest number of pairs of vertices that have the same edge.

Subgraphs of Multigraphs

A subgraph $H$ of a multigraph $G$ is a graph that is formed by selecting a subset of the vertices and edges of $G$ . The subgraph $H$ is said to be a proper subgraph of $G$ if it is not equal to $G$ . In other words, a proper subgraph is a subgraph that is smaller than the original graph.

Maximum Degree of Subgraphs

The maximum degree of a subgraph $H$ of a multigraph $G$ , denoted by $\Delta(H)$ , is the largest number of edges incident on any vertex in $H$ . In other words, it is the largest number of pairs of vertices in $H$ that have the same edge.

Decomposition of Multigraphs

A decomposition of a multigraph $G$ into two subgraphs $H$ and $G-H$ is a partition of the vertices and edges of $G$ into two sets, $H$ and $G-H$ . The subgraph $H$ is said to be a proper subgraph of $G$ if it is not equal to $G$ . In other words, a proper subgraph is a subgraph that is smaller than the original graph.

Condition on Sum of Maximum Degrees

The condition on the sum of maximum degrees of two subgraphs $H$ and $G-H$ is that the sum of their maximum degrees is at least $\Delta(G)$ . In other words, we want to find a decomposition of the multigraph $G$ into two subgraphs $H$ and $G-H$ such that the sum of their maximum degrees is at least $\Delta(G)$ .

Examples of Multigraphs

We will now provide some examples of multigraphs that satisfy the given condition. These examples will be constructed using graph theoretical techniques and computational methods.

Example 1: A Complete Multigraph

Let $G$ be a complete multigraph with $n$ vertices. In other words, every pair of vertices has an edge between them. The maximum degree of $G$ is $n-1$ , since every vertex has $n-1$ edges incident on it.

Example 2: A Cycle Multigraph

Let $G$ be a cycle multigraph with $n$ vertices. In other words, the vertices of $G$ form a cycle, and every pair of adjacent vertices has an edge between them. The maximum degree of $G$ is $2$ , since every vertex has two edges incident on it.

Example 3: A Tree Multigraph

Let $G$ be a tree multigraph with $n$ vertices. In other words, the vertices of $G$ form a tree, and every pair of adjacent vertices has an edge between them. The maximum degree of $G$ is $n-1$ , since every vertex has $n-1$ edges incident on it.

Conclusion

In this article, we have explored the problem of decomposing a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees. We have provided some examples of multigraphs that satisfy the given condition, and we have discussed the properties of these examples. We have also discussed the approach that we will use to tackle this problem, which involves a combination of graph theoretical techniques and computational methods.

Future Work

There are several directions that we can take this research in the future. Firstly, we can explore the properties of multigraphs that satisfy the given condition. Secondly, we can use computational methods to find more examples of multigraphs that satisfy the given condition. Finally, we can use graph algorithms to find the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees.

References

[1] Bondy, J. A., & Murty, U. S. R. (2008). Graph theory. Springer.
[2] Diestel, R. (2010). Graph theory. Springer.
[3] West, D. B. (2001). Introduction to graph theory. Prentice Hall.

Appendix

The following is a list of the notation used in this article:

$G$ : a multigraph
$\Delta(G)$ : the maximum degree of a multigraph $G$
$H$ : a subgraph of a multigraph $G$
$\Delta(H)$ : the maximum degree of a subgraph $H$
$G-H$ : the subgraph of $G$ that is not in $H$
$\Delta(G-H)$ : the maximum degree of the subgraph $G-H$
Q&A: Decomposing a Multigraph into Two Subgraphs with Condition on Sum of Maximum Degrees =====================================================================================

Introduction

In our previous article, we explored the problem of decomposing a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees. In this article, we will answer some of the most frequently asked questions about this problem.

Q: What is the motivation behind this problem?

A: The motivation behind this problem is to find a way to decompose a multigraph into two subgraphs with specific properties. This has applications in network design, where we want to partition a network into two subnetworks with specific properties.

Q: What is the condition on the sum of maximum degrees?

A: The condition on the sum of maximum degrees is that the sum of the maximum degrees of two subgraphs $H$ and $G-H$ is at least $\Delta(G)$ , where $\Delta(G)$ is the maximum degree of the multigraph $G$ .

Q: What are some examples of multigraphs that satisfy the given condition?

A: Some examples of multigraphs that satisfy the given condition include complete multigraphs, cycle multigraphs, and tree multigraphs.

Q: How can we find the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees?

A: We can use a combination of graph theoretical techniques and computational methods to find the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees.

Q: What are some of the challenges associated with this problem?

A: Some of the challenges associated with this problem include finding the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees, and verifying the results.

Q: What are some of the applications of this problem?

A: Some of the applications of this problem include network design, where we want to partition a network into two subnetworks with specific properties.

Q: What are some of the future directions for this research?

A: Some of the future directions for this research include exploring the properties of multigraphs that satisfy the given condition, using computational methods to find more examples of multigraphs that satisfy the given condition, and using graph algorithms to find the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees.

Q: What are some of the references that can be used to learn more about this problem?

A: Some of the references that can be used to learn more about this problem include [1], [2], and [3].

Q: What are some of the open problems associated with this research?

A: Some of the open problems associated with this research include finding the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees, and verifying the results.

Q: What are some of the tools that can be used to solve this problem?

A: Some of the tools that can be used to solve this problem include graph algorithms, computational methods, and graph theoretical techniques.

Q: What are some of the benefits of solving this problem?

A: Some of the benefits of solving this problem include finding a way to decompose a multigraph into two subgraphs with specific properties, and applying this to network design.

Q: What are some of the limitations of this problem?

A: Some of the limitations of this problem include the complexity of the problem, and the difficulty of finding the decomposition of a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees.

Q: What are some of the future applications of this research?

A: Some of the future applications of this research include network design, where we want to partition a network into two subnetworks with specific properties.

Conclusion

In this article, we have answered some of the most frequently asked questions about the problem of decomposing a multigraph into two subgraphs with a specific condition on the sum of their maximum degrees. We have also discussed some of the challenges associated with this problem, and some of the future directions for this research.

References

[1] Bondy, J. A., & Murty, U. S. R. (2008). Graph theory. Springer.
[2] Diestel, R. (2010). Graph theory. Springer.
[3] West, D. B. (2001). Introduction to graph theory. Prentice Hall.

Appendix

The following is a list of the notation used in this article:

$G$ : a multigraph
$\Delta(G)$ : the maximum degree of a multigraph $G$
$H$ : a subgraph of a multigraph $G$
$\Delta(H)$ : the maximum degree of a subgraph $H$
$G-H$ : the subgraph of $G$ that is not in $H$
$\Delta(G-H)$ : the maximum degree of the subgraph $G-H$