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On Tree-Connectivity and Path-Connectivity of Graphs
Graphs and Combinatorics ( IF 0.6 ) Pub Date : 2021-07-24 , DOI: 10.1007/s00373-021-02376-9
Shasha Li 1 , Zhongmei Qin 2 , Jianhua Tu 3 , Jun Yue 4
Affiliation  

Let G be a graph and k an integer with \(2\le k\le n\). The k -tree-connectivity of G, denoted by \(\kappa _k(G)\), is defined as the minimum \(\kappa _G(S)\) over all k-subsets S of vertices, where \(\kappa _G(S)\) denotes the maximum number of internally disjoint S-trees in G. The k -path-connectivity of G, denoted by \(\pi _k(G)\), is defined as the minimum \(\pi _G(S)\) over all k-subsets S of vertices, where \(\pi _G(S)\) denotes the maximum number of internally disjoint S-paths in G. In this paper, we first prove that for any fixed integer \(k\ge 1\), given a graph G and a subset S of V(G), deciding whether \(\pi _G(S)\ge k\) is \(\mathcal {NP}\)-complete. Moreover, we also show that for any fixed integer \(k_1\ge 5\), given a graph G, a \(k_1\)-subset S of V(G) and an integer \(1\le k_2\le n-1\), deciding whether \(\pi _G(S)\ge k_2\) is \(\mathcal {NP}\)-complete. Let \(\pi (k,\ell )=1+\max \{\kappa (G)|\ \)G\(\text {\ is\ a\ graph\ with}\ \pi _k(G)< \ell \}\). Hager (Discrete Math 59:53–59, 1986) showed that \(\ell (k-1)\le \pi (k,\ell )\le 2^{k-2}\ell\) and conjectured that \(\pi (k,\ell )=\ell (k-1)\) for \(k\ge 2\) and \(\ell \ge 1\). He also confirmed the conjecture for \(2\le k\le 4\) and proved \(\pi (5,\ell )\le \lceil \frac{9}{2}\ell \rceil\). By introducing a “Generalized Path-Bundle Transformation”, we confirm the conjecture for \(k=5\) and prove that \(\pi (k,\ell )\le 2^{k-3}\ell\) for \(k\ge 5\) and \(\ell \ge 1\). By employing this transformation, we also prove that if G is a graph with \(\kappa (G)\ge (k-1)\ell\) for any \(k\ge 2\) and \(\ell \ge 1\), then \(\kappa _k(G)\ge \ell\).



中文翻译:

关于图的树连通性和路径连通性

G是一个图,k是一个整数,其中\(2\le k\le n\)Gk 树连通性,用\(\kappa _k(G)\) 表示,定义为顶点的所有k 子S上的最小值\(\kappa _G(S)\),其中\(\ kappa _G(S)\)表示G中内部不相交的S树的最大数量。Gk路径连通性,表示为\(\pi _k(G)\),定义为所有k 上的最小值\(\pi _G(S)\) 顶点的-subsets S,其中\(\pi _G(S)\)表示G中内部不相交的S -paths的最大数量。在本文中,我们首先证明,对于任何固定的整数\(K \ GE 1 \)给定图ģ和一个子集小号VG ^),决定是否\(\ PI _G(S)\锗的K \)\(\mathcal {NP}\) -完成的。此外,我们还表明,对于任何固定的整数\(K_1 \ GE 5 \) ,给定图ģ,一个\(K_1 \) -subset小号VG ^) 和一个整数\(1\le k_2\le n-1\),决定\(\pi _G(S)\ge k_2\)是否是\(\mathcal {NP}\) -完全的。设\(\pi (k,\ell )=1+\max \{\kappa (G)|\ \) G \(\text {\ is\ a\ graph\ with}\ \pi _k(G)< \ell \}\)。Hager (Discrete Math 59:53–59, 1986) 证明\(\ell (k-1)\le \pi (k,\ell )\le 2^{k-2}\ell\)并推测\ (\pi (k,\ell )=\ell (k-1)\)用于\(k\ge 2\)\(\ell \ge 1\)。他还证实了\(2\le k\le 4\)的猜想并证明了\(\pi (5,\ell )\le \lceil \frac{9}{2}\ell \rceil\). 通过引入“广义路径束变换”,我们证实了\(k=5\)的猜想,并证明了\(\pi (k,\ell )\le 2^{k-3}\ell\)对于\(k\ge 5\)\(\ell \ge 1\)。通过使用这种变换,我们还证明了如果G是一个具有\(\kappa (G)\ge (k-1)\ell\)对于任何\(k\ge 2\)\(\ell \ge 1\),然后\(\kappa _k(G)\ge \ell\)

更新日期:2021-07-24
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