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| Natura: | Preprint |
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2025
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| Accesso online: | https://arxiv.org/abs/2502.19682 |
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| _version_ | 1866915175539408896 |
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| author | Dai, Tianjiao Liu, Weichan Zhang, Xin |
| author_facet | Dai, Tianjiao Liu, Weichan Zhang, Xin |
| contents | In an $r$-partite graph, an independent transversal of size $s$ (ITS) consists of $s$ vertices from each part forming an independent set. Motivated by a question from Bollobás, Erdős, and Szemerédi (1975), Di Braccio and Illingworth (2024) inquired about the minimum degree needed to ensure an $n \times \cdots \times n$ $r$-partite graph contains $K_r(s)$, a complete $r$-partite graph with $s$ vertices in each part. We reformulate this as finding the smallest $n$ such that any $n \times \cdots \times n$ $r$-partite graph with maximum degree $Δ$ has an ITS. For any $\varepsilon>0$, we prove the existence of a $γ>0$ ensuring that if $G$ is a multipartite graph partitioned as $(V_1, V_2, \ldots, V_r)$, where the average degree of each part $V_i$ is at most $D$, the maximum degree of any vertex to any part $V_i$ is at most $γD$, and the size of each part $V_i$ is at least $(s + \varepsilon)D$, then $G$ possesses an ITS. The constraint $(s + \varepsilon)D$ on the part size is tight. This extends results of Loh and Sudakov (2007), Glock and Sudakov (2022), and Kang and Kelly (2022). We also show that any $n \times \cdots \times n$ $r$-partite graph with minimum degree at least $\left(r-1-\frac{1}{2s^2}\right)n$ contains $K_r(s)$ and provide a relative Turán-type result. Additionally, this paper explores counting ITSs in multipartite graphs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_19682 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Independent transversal blow-up of graphs Dai, Tianjiao Liu, Weichan Zhang, Xin Combinatorics Discrete Mathematics In an $r$-partite graph, an independent transversal of size $s$ (ITS) consists of $s$ vertices from each part forming an independent set. Motivated by a question from Bollobás, Erdős, and Szemerédi (1975), Di Braccio and Illingworth (2024) inquired about the minimum degree needed to ensure an $n \times \cdots \times n$ $r$-partite graph contains $K_r(s)$, a complete $r$-partite graph with $s$ vertices in each part. We reformulate this as finding the smallest $n$ such that any $n \times \cdots \times n$ $r$-partite graph with maximum degree $Δ$ has an ITS. For any $\varepsilon>0$, we prove the existence of a $γ>0$ ensuring that if $G$ is a multipartite graph partitioned as $(V_1, V_2, \ldots, V_r)$, where the average degree of each part $V_i$ is at most $D$, the maximum degree of any vertex to any part $V_i$ is at most $γD$, and the size of each part $V_i$ is at least $(s + \varepsilon)D$, then $G$ possesses an ITS. The constraint $(s + \varepsilon)D$ on the part size is tight. This extends results of Loh and Sudakov (2007), Glock and Sudakov (2022), and Kang and Kelly (2022). We also show that any $n \times \cdots \times n$ $r$-partite graph with minimum degree at least $\left(r-1-\frac{1}{2s^2}\right)n$ contains $K_r(s)$ and provide a relative Turán-type result. Additionally, this paper explores counting ITSs in multipartite graphs. |
| title | Independent transversal blow-up of graphs |
| topic | Combinatorics Discrete Mathematics |
| url | https://arxiv.org/abs/2502.19682 |