运筹学学报(中英文) ›› 2025, Vol. 29 ›› Issue (1): 198-206.doi: 10.15960/j.cnki.issn.1007-6093.2025.01.016

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单圈图的零强迫和全强迫

李宝欣1, 计省进1,*()   

  1. 1. 山东理工大学数学与统计学院, 山东淄博 255000
  • 收稿日期:2021-07-20 出版日期:2025-03-15 发布日期:2025-03-08
  • 通讯作者: 计省进 E-mail:jishengjin@sdut.edu.cn
  • 基金资助:
    山东省自然科学基金(ZR2019MA012)

Total forcing and zero forcing of unicyclic graphs

Baoxin LI1, Shengjin JI1,*()   

  1. 1. School of Mathematics and Statistics, Shandong University of Technology, Zibo 255000, Shandong, China
  • Received:2021-07-20 Online:2025-03-15 Published:2025-03-08
  • Contact: Shengjin JI E-mail:jishengjin@sdut.edu.cn

摘要:

SV是一个初始着色顶点子集, 它的所有顶点都着黑色, S中的每个顶点称为S-着色, G中所有其他未着色的顶点称为S-未着色。若一个着黑色的顶点v恰好只有一个未着色的邻点u, 则v强迫顶点u着黑色, 这样的过程称为强迫过程。如果从一个初始顶点集S出发, 逐步运用强迫过程直到G中所有的顶点都变成黑色, 则称这个初始集SG的零强迫集(强迫集)。G的零强迫集的最小基数用F(G)表示, 称为G的零强迫数。如果SG中的导出子图G[S]不包含孤立顶点, 则强迫集S称为G的全强迫集, 全强迫集的最小基数用Ft(G)表示, 称为G的全强迫数。注意到零强迫数和全强迫数有如下关系, F(G)Ft(G)2F(G)。刻画满足F(G)Ft(G)或者2F(G)Ft(G)的图G是有意义的。基于此, 本文在单圈图上刻画了满足F(G)Ft(G)的所有图G。此外, 本文研究了给定匹配数为k的单圈图G的零强迫数的上界, 即F(G)nk, 等号成立当且仅当GC4,A0。此外, 当GC4,A0时, 本文刻画了使得F(G)=nk1的所有图G

关键词: 单圈图, 零强迫, 全强迫, 匹配

Abstract:

Let SV be an initial vertex subset of coloring, and all vertices of SV are black. Each vertex in S is called S-colored, and all other vertices in G are called S-uncolored. If a vertex v with black color has just one uncolored neighbor u, then v forces the vertex u to be black. Such a process is called forcing process. The initial set S is called a zero forcing set (forcing set) of G if, by iteratively applying the forcing process, every vertex in G becomes black. The minimum cardinality of a zero forcing set in G is zero forcing number, denoted F(G). If the induced subgraph G[S] does not contain isolated vertices, then S is called a total forcing set of G, and the minimum cardinality of a total forcing set in G is total forcing number, denoted Ft(G). Note that zero forcing number and total forcing number of graph G has the relation, F(G)Ft(G)2F(G). Hence, it is interesting and meaningful to characterize all graphs satisfying F(G)=Ft(G) or 2F(G)=Ft(G). In this paper, we study all graphs G satisfying F(G)=Ft(G) in unicyclic graphs. In addition, we discuss the upper bound of zero forcing number in all unicyclic graphs with given matching number k, and show that F(G)nk and equality holds if and only if GC4,A0. Moreover, we characterize all graphs such that their forcing number equal to nk1 if GC4,A0.

Key words: unicyclic graph, zero forcing, total forcing, matching

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