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Embedding k-Factors in Quasi-Random Hypergraphs

This study examines conditions for embedding k-factors in k-partite hypergraphs.

― 5 min read


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Table of Contents

In the world of mathematics, there are many interesting questions about graphs and how they can be formed or arranged. One area of study focuses on combining certain types of graphs, known as Hypergraphs, especially those that have a specific structure called "partite." This paper looks at a special kind of problem involving these graphs, particularly when looking to create what is called a "factor."

What is a Hypergraph?

A hypergraph is a generalization of a regular graph. In a regular graph, edges connect pairs of vertices. In a hypergraph, edges can connect any number of vertices. For example, if we have a group of friends, a hypergraph could represent friendships among groups, not just pairs. When we say a hypergraph is "k-partite," it means we can divide the vertices into groups, and edges can only connect vertices from different groups.

Understanding Factors in Graphs

A factor is a way of breaking a graph into smaller parts that still hold certain properties of the original graph. Specifically, when we refer to a k-factor of a hypergraph, we mean a collection of smaller hypergraphs that cover the entire vertex set exactly once, without overlapping.

Why Study Quasi-Random Graphs?

Quasi-random graphs are those that seem to behave randomly within certain constraints. They are interesting because they provide insights into how regularity can emerge from what appears to be chaos. Studying these graphs can give us a deeper understanding of the balance between structure and randomness.

The Minimum Degree Condition

When discussing hypergraphs, we often talk about degrees, which indicate how many edges are connected to a vertex. The minimum degree condition is a requirement that ensures each vertex has a certain number of edges. This condition helps in finding factors because it guarantees that there are enough edges to connect the vertices appropriately.

Previous Research

Many studies have explored factors in quasi-random graphs. Earlier works laid the groundwork for the current understanding of how these factors can be arranged, providing essential density conditions for embedding them within these graphs.

The Main Problem

The main focus of this study is to determine how to embed K-factors in k-partite quasi-random hypergraphs under specific conditions related to density and the minimum degree of vertices. This means we want to know under what circumstances we can form these smaller, balanced structures from larger, complex graphs.

Key Findings

Conditions for Embedding k-Factors

This research finds that if you have a k-partite hypergraph with a sufficient number of vertices in each part and certain density conditions, you will be able to find a k-factor. This is crucial because it means that under the right conditions, it is always possible to break down the graph into smaller pieces that fit together perfectly.

The Role of Minimum Codegree

The minimum codegree is a stronger condition than just looking at the minimum degree of individual vertices. It focuses on pairs of vertices and how many edges can connect them. The findings suggest that this codegree is essential for ensuring all types of k-partite factors are included in the larger hypergraph.

Adjustments to Conventional Wisdom

The study challenges some earlier beliefs about the conditions necessary for finding factors in graphs. It shows that the previously accepted restrictions can be relaxed under certain circumstances, broadening the understanding of graph structures and their complexities.

The Importance of Density

The density of a graph is a measure of how many edges it contains relative to the maximum number of edges possible. A denser graph provides more connections and, thus, more opportunities for forming k-factors. The research emphasizes that higher density dramatically increases the likelihood of successfully embedding k-factors.

Examples and Illustrations

To better understand these concepts, consider real-life situations like organizing teams for activities. Each team needs to include members from different groups, and ensuring that each group has a sufficient number of representatives is akin to maintaining the right density in a hypergraph to allow for a balanced factor.

Constructing Graphs with Desired Properties

The study presents methods for constructing hypergraphs that meet the set conditions. By employing a probabilistic approach, the research outlines techniques for generating these graphs effectively. This is particularly useful for mathematicians and computer scientists working on problems involving large datasets or networked systems.

Implications of Findings

The results of this study have implications not only for theoretical mathematics but also for practical applications in fields such as computer science, social network analysis, and biology. Understanding how to properly embed factors within complex structures can lead to better algorithms and models that reflect real-world systems.

Future Directions

The research indicates several paths for future investigation. Further exploration could examine other types of hypergraphs, different Densities, or additional conditions like edge weights. There is also a need to apply these theoretical findings to real-world problems, allowing practitioners to utilize the frameworks built from this research.

Conclusion

The exploration of embedding k-factors in k-partite quasi-random hypergraphs opens new avenues for understanding complex structures in mathematics and related fields. By establishing clear conditions for successful embedding and exploring the fundamental ideas of density and codegree, this work contributes significantly to both the theory and practice of graph theory. The findings are a step toward unraveling the complexities of hypergraph structures, enhancing our ability to analyze and understand intricate systems.

Original Source

Title: Tilings in quasi-random $k$-partite hypergraphs

Abstract: Given $k\ge 2$ and two $k$-graphs ($k$-uniform hypergraphs) $F$ and $H$, an $F$-factor in $H$ is a set of vertex disjoint copies of $F$ that together cover the vertex set of $H$. Lenz and Mubayi were first to study the $F$-factor problems in quasi-random $k$-graphs with a minimum degree condition. Recently, Ding, Han, Sun, Wang and Zhou gave the density threshold for having all $3$-partite $3$-graphs factors in quasi-random $3$-graphs with vanishing minimum codegree condition $\Omega(n)$. In this paper, we consider embedding factors when the host $k$-graph is $k$-partite and quasi-random with partite minimum codegree condition. We prove that if $p>1/2$ and $F$ is a $k$-partite $k$-graph with each part having $m$ vertices, then for $n$ large enough and $m\mid n$, any $p$-dense $k$-partite $k$-graph with each part having $n$ vertices and partite minimum codegree condition $\Omega(n)$ contains an $F$-factor. We also present a construction showing that $1/2$ is best possible. Furthermore, for $1\leq \ell \leq k-2$, by constructing a sequence of $p$-dense $k$-partite $k$-graphs with partite minimum $\ell$-degree $\Omega(n^{k-\ell})$ having no $K_k(m)$-factor, we show that the partite minimum codegree constraint can not be replaced by other partite minimum degree conditions. On the other hand, we prove that $n/2$ is the asymptotic partite minimum codegree threshold for having all fixed $k$-partite $k$-graph factors in sufficiently large host $k$-partite $k$-graphs even without quasi-randomness.

Authors: Shumin Sun

Last Update: 2023-06-18 00:00:00

Language: English

Source URL: https://arxiv.org/abs/2306.10539

Source PDF: https://arxiv.org/pdf/2306.10539

Licence: https://creativecommons.org/licenses/by/4.0/

Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.

Thank you to arxiv for use of its open access interoperability.

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