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arXiv 2209.08946math.CO
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关于图的定向的Wiener指标

On the Wiener Index of Orientations of Graphs

Peter Dankelmann

摘要:

强有向图$D$的Wiener指标定义为所有有序顶点对之间的距离之和。如果在$D$中不存在从$a$到$b$的路径,则通过将从顶点$a$到顶点$b$的距离定义为$0$,该定义已被扩展到不一定是强的有向图。Knor,uSkrekovski和Tepeh [关于定向图的Wiener指标的一些注记.应用程序\数学。计算。\ { \bf 273}]考虑了具有最大Wiener指数的图的方向。证明了对于给定的树$T$,Wiener指数最大的$T$的方向$D$总是包含一个顶点$v$,使得对于每个顶点$u$,在$D$中要么有一条$(u,v)$ -路,要么有一条$(v,u)$ -路.在本文中,我们反驳了猜想。我们还证明了寻找给定图的最大Wiener指数的方向的问题是NP-完全的,从而回答了Knor,uSkrekovski和Tepeh [Orientations of graphs with maximum Wiener index.离散应用程序\数学。211]。我们简要地讨论了相应的问题,找到一个方向的最小维纳指数给定的图,并证明了特殊情况下,如果一个给定的图$m$边缘有一个方向的维纳指数$m$可以解决在$n$的时间二次。

英文摘要:

The Wiener index of a strong digraph $D$ is defined as the sum of the distances between all ordered pairs of vertices. This definition has been extended to digraphs that are not necessarily strong by defining the distance from a vertex $a$ to a vertex $b$ as $0$ if there is no path from $a$ to $b$ in $D$. Knor, uSkrekovski and Tepeh [Some remarks on Wiener index of oriented graphs. Appl.\ Math.\ Comput.\ {\bf 273}] considered orientations of graphs with maximum Wiener index. The authors conjectured that for a given tree $T$, an orientation $D$ of $T$ of maximum Wiener index always contains a vertex $v$ such that for every vertex $u$, there is either a $(u,v)$-path or a $(v,u)$-path in $D$. In this paper we disprove the conjecture. We also show that the problem of finding an orientation of maximum Wiener index of a given graph is NP-complete, thus answering a question by Knor, uSkrekovski and Tepeh [Orientations of graphs with maximum Wiener index. Discrete Appl.\ Math.\ 211]. We briefly discuss the corresponding problem of finding an orientation of minimum Wiener index of a given graph, and show that the special case of deciding if a given graph on $m$ edges has an orientation of Wiener index $m$ can be solved in time quadratic in $n$.

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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