Constructing disjoint Steiner trees in Sierpiński graphs

Abstract

Let $G$ be a graph and $S\subseteq V(G)$ with $|S|\ge 2$. Then the trees $T_1,T_2,\cdots ,T_{\ell }$ in $G$ are \emph{internally disjoint Steiner trees} connecting $S$ (or $S$-Steiner trees) if $E(T_i)\cap E(T_j)=\varnothing$ and $V(T_i)\cap V(T_j)=S$ for every pair of distinct integers $i,j$, $1\le i,j\le \ell$. Similarly, if we only have the condition $E(T_i)\cap E(T_j)=\varnothing$ but without the condition $V(T_i)\cap V(T_j)=S$, then they are \emph{edge-disjoint Steiner trees}. The \emph{generalized $k$-connectivity}, denoted by $\hat{I}{º}_k(G)$, of a graph $G$, is defined as $\hat{I}{º}_k(G)=\min \{\hat{I}{º}_G(S)|S\subseteq V(G)\text{and}|S|=k\}$, where $\hat{I}{º}_G(S)$ is the maximum number of internally disjoint $S$-Steiner trees. The \emph{generalized local edge-connectivity} $\hat{I}{»}_G(S)$ is the maximum number of edge-disjoint Steiner trees connecting $S$ in $G$. The {\it generalized $k$-edge-connectivity} $\hat{I}{»}_k(G)$ of $G$ is defined as $\hat{I}{»}_k(G)=\min \{\hat{I}{»}_G(S)|S\subseteq V(G)and|S|=k\}$. These measures are generalizations of the concepts of connectivity and edge-connectivity, and they and can be used as measures of vulnerability of networks. It is, in general, difficult to compute these generalized connectivities. However, there are precise results for some special classes of graphs. In this paper, we obtain the exact value of $\hat{I}{»}_k(S(n,\ell ))$ for $3\le k\le {\ell }^n$, and the exact value of $\hat{I}{º}_k(S(n,\ell ))$ for $3\le k\le \ell$, where $S(n,\ell )$ is the Sierpiński graphs with order ${\ell }^n$. As a direct consequence, these graphs provide additional interesting examples when $\hat{I}{»}_k(S(n,\ell ))=\hat{I}{º}_k(S(n,\ell ))$. We also study the some network properties of Sierpiński graphs.

Steiner Tree; Generalized Connectivity; Sierpiński Graph