Path connectivity of line graphs

Dirac showed that in a $(k-1)$-connected graph there is a path through each $k$ vertices. The path $k$-connectivity $\pi_k(G)$ of a graph $G$, which is a generalization of Dirac's notion, was introduced by Hager in 1986. In this paper, we study path connectivity of line graphs.Comment: 15 pages. arXiv admin note: substantial text overlap with arXiv:1508.07202, arXiv:1207.1838; text overlap with arXiv:1103.6095 by other author

The minimal size of graphs with given pendant-tree connectivity

The concept of pendant-tree $k$-connectivity $\tau_k(G)$ of a graph $G$, introduced by Hager in 1985, is a generalization of classical vertex-connectivity. Let $f(n,k,\ell)$ be the minimal number of edges of a graph $G$ of order $n$ with $\tau_k(G)=\ell \ (1\leq \ell\leq n-k)$. In this paper, we give some exact value or sharp bounds of the parameter $f(n,k,\ell)$.Comment: 19 pages. arXiv admin note: substantial text overlap with arXiv:1508.07202, arXiv:1508.07149, arXiv:1603.03995, arXiv:1604.01887; text overlap with arXiv:1103.6095 by other author

Steiner 3-diameter, maximum degree and size of a graph

The Steiner $k$-diameter $sdiam_k(G)$ of a graph $G$, introduced by Chartrand, Oellermann, Tian and Zou in 1989, is a natural generalization of the concept of classical diameter. When $k=2$, $sdiam_2(G)=diam(G)$ is the classical diameter. The problem of determining the minimum size of a graph of order $n$ whose diameter is at most $d$ and whose maximum is $\ell$ was first introduced by Erd\"{o}s and R\'{e}nyi. In this paper, we generalize the above problem for Steiner $k$-diameter, and study the problem of determining the minimum size of a graph of order $n$ whose Steiner $3$-diameter is at most $d$ and whose maximum is at most $\ell$.Comment: 23 pages, 5 figures. arXiv admin note: text overlap with arXiv:1703.03984, arXiv:1703.0141

On the pedant tree-connectivity of graphs

The concept of pedant tree-connectivity was introduced by Hager in 1985. For a graph $G=(V,E)$ and a set $S\subseteq V(G)$ of at least two vertices, \emph{an $S$-Steiner tree} or \emph{a Steiner tree connecting $S$} (or simply, \emph{an $S$-tree}) is a such subgraph $T=(V',E')$ of $G$ that is a tree with $S\subseteq V'$. For an $S$-Steiner tree, if the degree of each vertex in $S$ is equal to one, then this tree is called a \emph{pedant $S$-Steiner tree}. Two pedant $S$-Steiner trees $T$ and $T'$ are said to be \emph{internally disjoint} if $E(T)\cap E(T')=\varnothing$ and $V(T)\cap V(T')=S$. For $S\subseteq V(G)$ and $|S|\geq 2$, the \emph{local pedant-tree connectivity} $\tau_G(S)$ is the maximum number of internally disjoint pedant $S$-Steiner trees in $G$. For an integer $k$ with $2\leq k\leq n$, \emph{$k$-pedant tree-connectivity} is defined as $\tau_k(G)=\min\{\tau_G(S)\,|\,S\subseteq V(G),|S|=k\}$. In this paper, we first study the sharp bounds of pedant tree-connectivity. Next, we obtain the exact value of a threshold graph, and give an upper bound of the pedant-tree $k$-connectivity of a complete multipartite graph. For a connected graph $G$, we show that $0\leq \tau_k(G)\leq n-k$, and graphs with $\tau_k(G)=n-k,n-k-1,n-k-2,0$ are characterized in this paper. In the end, we obtain the Nordhaus-Guddum type results for pedant tree-connectivity.Comment: 25 page

Pendant-tree connectivity of line graphs

The concept of pendant-tree connectivity, introduced by Hager in 1985, is a generalization of classical vertex-connectivity. In this paper, we study pendant-tree connectivity of line graphs.Comment: 19 pagers, 2 figures. arXiv admin note: substantial text overlap with arXiv:1603.03995, arXiv:1508.07202, arXiv:1508.07149. text overlap with arXiv:1103.6095 by other author

Constructing Internally Disjoint Pendant Steiner Trees in Cartesian Product Networks

The concept of pedant tree-connectivity was introduced by Hager in 1985. For a graph $G=(V,E)$ and a set $S\subseteq V(G)$ of at least two vertices, \emph{an $S$-Steiner tree} or \emph{a Steiner tree connecting $S$} (or simply, \emph{an $S$-tree}) is a such subgraph $T=(V',E')$ of $G$ that is a tree with $S\subseteq V'$. For an $S$-Steiner tree, if the degree of each vertex in $S$ is equal to one, then this tree is called a \emph{pedant $S$-Steiner tree}. Two pedant $S$-Steiner trees $T$ and $T'$ are said to be \emph{internally disjoint} if $E(T)\cap E(T')=\varnothing$ and $V(T)\cap V(T')=S$. For $S\subseteq V(G)$ and $|S|\geq 2$, the \emph{local pedant tree-connectivity} $\tau_G(S)$ is the maximum number of internally disjoint pedant $S$-Steiner trees in $G$. For an integer $k$ with $2\leq k\leq n$, \emph{pedant tree $k$-connectivity} is defined as $\tau_k(G)=\min\{\tau_G(S)\,|\,S\subseteq V(G),|S|=k\}$. In this paper, we prove that for any two connected graphs $G$ and $H$, $\tau_3(G\Box H)\geq \min\{3\lfloor\frac{\tau_3(G)}{2}\rfloor,3\lfloor\frac{\tau_3(H)}{2}\rfloor\}$. Moreover, the bound is sharp.Comment: 22 page

The Steiner diameter of a graph

The Steiner distance of a graph, introduced by Chartrand, Oellermann, Tian and Zou in 1989, is a natural generalization of the concept of classical graph distance. For a connected graph $G$ of order at least $2$ and $S\subseteq V(G)$, the \emph{Steiner distance} $d(S)$ among the vertices of $S$ is the minimum size among all connected subgraphs whose vertex sets contain $S$. Let $n,k$ be two integers with $2\leq k\leq n$. Then the \emph{Steiner $k$-eccentricity $e_k(v)$} of a vertex $v$ of $G$ is defined by $e_k(v)=\max \{d(S)\,|\,S\subseteq V(G), \ |S|=k, \ and \ v\in S \}$. Furthermore, the \emph{Steiner $k$-diameter} of $G$ is $sdiam_k(G)=\max \{e_k(v)\,|\, v\in V(G)\}$. In 2011, Chartrand, Okamoto and Zhang showed that $k-1\leq sdiam_k(G)\leq n-1$. In this paper, graphs with $sdiam_3(G)=2,3,n-1$ are characterized, respectively. We also consider the Nordhaus-Gaddum-type results for the parameter $sdiam_k(G)$. We determine sharp upper and lower bounds of $sdiam_k(G)+sdiam_k(\overline{G})$ and $sdiam_k(G)\cdot sdiam_k(\overline{G})$ for a graph $G$ of order $n$. Some graph classes attaining these bounds are also given.Comment: 14 page

Nordhaus-Gaddum-type results for the generalized edge-connectivity of graphs

Let $G$ be a graph, $S$ be a set of vertices of $G$, and $\lambda(S)$ be the maximum number $\ell$ of pairwise edge-disjoint trees $T_1, T_2,..., T_{\ell}$ in $G$ such that $S\subseteq V(T_i)$ for every $1\leq i\leq \ell$. The generalized $k$-edge-connectivity $\lambda_k(G)$ of $G$ is defined as $\lambda_k(G)= min\{\lambda(S) | S\subseteq V(G) \ and \ |S|=k\}$. Thus $\lambda_2(G)=\lambda(G)$. In this paper, we consider the Nordhaus-Gaddum-type results for the parameter $\lambda_k(G)$. We determine sharp upper and lower bounds of $\lambda_k(G)+\lambda_k(\bar{G})$ and $\lambda_k(G)... \lambda_k(\bar{G})$ for a graph $G$ of order $n$, as well as for a graph of order $n$ and size $m$. Some graph classes attaining these bounds are also given.Comment: 16 page

A survey on the generalized connectivity of graphs

The generalized $k$-connectivity $\kappa_k(G)$ of a graph $G$ was introduced by Hager before 1985. As its a natural counterpart, we introduced the concept of generalized edge-connectivity $\lambda_k(G)$, recently. In this paper we summarize the known results on the generalized connectivity and generalized edge-connectivity. After an introductory section, the paper is then divided into nine sections: the generalized (edge-)connectivity of some graph classes, algorithms and computational complexity, sharp bounds of $\kappa_k(G)$ and $\lambda_k(G)$, graphs with large generalized (edge-)connectivity, Nordhaus-Gaddum-type results, graph operations, extremal problems, and some results for random graphs and multigraphs. It also contains some conjectures and open problems for further studies.Comment: 51 pages. arXiv admin note: text overlap with arXiv:1303.3881 by other author

Steiner diameter, maximum degree and size of a graph

The Steiner diameter $sdiam_k(G)$ of a graph $G$, introduced by Chartrand, Oellermann, Tian and Zou in 1989, is a natural generalization of the concept of classical diameter. When $k=2$, $sdiam_2(G)=diam(G)$ is the classical diameter. The problem of determining the minimum size of a graph of order $n$ whose diameter is at most $d$ and whose maximum is $\ell$ was first introduced by Erd\"{o}s and R\'{e}nyi. Recently, Mao considered the problem of determining the minimum size of a graph of order $n$ whose Steiner $k$-diameter is at most $d$ and whose maximum is at most $\ell$, where $3\leq k\leq n$, and studied this new problem when $k=3$. In this paper, we investigate the problem when $n-3\leq k\leq n$.Comment: 24 pages, 5 figures. arXiv admin note: text overlap with arXiv:1703.0141