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arXiv 2406.04020math.CO
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导出匹配与边开 packing:树与积图

Induced matching vs edge open packing: trees and product graphs

Bostjan Bresar, Tanja Dravec, Jaka Hedzet, Babak Samadi

AI总结:

本文研究了图的边开 packing 数与导出匹配数的关系,刻画了等式成立的树结构,并推导了多种积图(字典积、直积、笛卡尔积、强积、根积)上这两个不变量的精确值或紧下界。

摘要:

给定图 $G$,其每个连通分支均为星图的导出子图的最大规模称为 $G$ 的边开 packing 数 $ρ_{e}^{o}(G)$。类似地,每个连通分支均为星图 $K_{1,1}$ 的导出子图的最大规模称为 $G$ 的导出匹配数 $ν_I(G)$。虽然不等式 $ρ_e^o(G)\geq ν_{I}(G)$ 对所有图 $G$ 显然成立,我们给出了达到等式条件的树的结构刻画。我们证明任意两图 $G$ 和 $H$ 的字典积 $G\circ H$ 的导出匹配数等于 $α(G)ν_I(H)$。利用类似技术,我们证明了图的字典积边开 packing 数的紧下界和上界,这特别导致了在三角图中本文研究的两个不变量的 NP-hardness 结果。对于两图的直积 $G\times H$,我们给出了 $ν_I(G\times H)$ 和 $ρ_{e}^{o}(G\times H)$ 的下界,两者均被广泛证明是紧的。我们还给出了两图的笛卡尔积和强积中这两个不变量的紧下界。最后,我们考虑超立方体中的边开 packing 数,确定了当 $n$ 是 $2$ 的幂时 $ρ_e^o(Q_n)$ 的精确值,并给出了任意两图在任意根顶点上的根积的导出匹配数的闭式公式。

英文摘要:

Given a graph $G$, the maximum size of an induced subgraph of $G$ each component of which is a star is called the edge open packing number, $ρ_{e}^{o}(G)$, of $G$. Similarly, the maximum size of an induced subgraph of $G$ each component of which is the star $K_{1,1}$ is the induced matching number, $ν_I(G)$, of $G$. While the inequality $ρ_e^o(G)\geq ν_{I}(G)$ clearly holds for all graphs $G$, we provide a structural characterization of those trees that attain the equality. We prove that the induced matching number of the lexicographic product $G\circ H$ of arbitrary two graphs $G$ and $H$ equals $α(G)ν_I(H)$. By similar techniques, we prove sharp lower and upper bounds on the edge open packing number of the lexicographic product of graphs, which in particular lead to NP-hardness results in triangular graphs for both invariants studied in this paper. For the direct product $G\times H$ of two graphs we provide lower bounds on $ν_I(G\times H)$ and $ρ_{e}^{o}(G\times H)$, both of which are widely sharp. We also present sharp lower bounds for both invariants in the Cartesian and the strong product of two graphs. Finally, we consider the edge open packing number in hypercubes establishing the exact values of $ρ_e^o(Q_n)$ when $n$ is a power of $2$, and present a closed formula for the induced matching number of the rooted product of arbitrary two graphs over an arbitrary root vertex.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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