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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2504.09159 |
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| _version_ | 1866915811521724416 |
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| author | Wu, Hailun Zhang, Heping |
| author_facet | Wu, Hailun Zhang, Heping |
| contents | For a positive integer $d$, a $d$-transversal set of a graph $G$ is an edge subset $T\subseteq E(G)$ such that $|T\cap M|\geq d$ for every maximum matching $M$ of $G$. The $d$-transversal number of $G$, denoted by $τ_d(G)$, is the minimum cardinality of a $d$-transversal set in $G$. It is NP-complete to determine the $d$-transversal number of a bipartite graph for any fixed $d\geq 1$. Ries et al. (Discrete Math. 310 (2010) 132-146) established the $d$-transversal number of rectangular grids $P_m\square P_n$. In this paper, we consider cylindrical grids $P_m\square C_n$ and toroidal grids $C_m\square C_n$. We derive explicit expressions for the $d$-transversal numbers of $P_m\square C_n$ for $m\geq 1$ and even $n\geq 4$, or even $m\geq 2$ and $n=3$, and of $C_m\square C_n$ with even order, for $1\leq d\leq \frac{mn}{2}$. For the other cases we obtain explicit expressions or bounds for their $d$-transversal numbers. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_09159 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | On the $d$-transversal number of cylindrical and toroidal grids Wu, Hailun Zhang, Heping Combinatorics For a positive integer $d$, a $d$-transversal set of a graph $G$ is an edge subset $T\subseteq E(G)$ such that $|T\cap M|\geq d$ for every maximum matching $M$ of $G$. The $d$-transversal number of $G$, denoted by $τ_d(G)$, is the minimum cardinality of a $d$-transversal set in $G$. It is NP-complete to determine the $d$-transversal number of a bipartite graph for any fixed $d\geq 1$. Ries et al. (Discrete Math. 310 (2010) 132-146) established the $d$-transversal number of rectangular grids $P_m\square P_n$. In this paper, we consider cylindrical grids $P_m\square C_n$ and toroidal grids $C_m\square C_n$. We derive explicit expressions for the $d$-transversal numbers of $P_m\square C_n$ for $m\geq 1$ and even $n\geq 4$, or even $m\geq 2$ and $n=3$, and of $C_m\square C_n$ with even order, for $1\leq d\leq \frac{mn}{2}$. For the other cases we obtain explicit expressions or bounds for their $d$-transversal numbers. |
| title | On the $d$-transversal number of cylindrical and toroidal grids |
| topic | Combinatorics |
| url | https://arxiv.org/abs/2504.09159 |