scholarly journals Component factors and binding number conditions in graphs

2021 ◽  
Vol 6 (11) ◽  
pp. 12460-12470
Author(s):  
Sizhong Zhou ◽  
◽  
Jiang Xu ◽  
Lan Xu ◽  

<abstract><p>Let $ G $ be a graph. For a set $ \mathcal{H} $ of connected graphs, an $ \mathcal{H} $-factor of a graph $ G $ is a spanning subgraph $ H $ of $ G $ such that every component of $ H $ is isomorphic to a member of $ \mathcal{H} $. A graph $ G $ is called an $ (\mathcal{H}, m) $-factor deleted graph if for every $ E'\subseteq E(G) $ with $ |E'| = m $, $ G-E' $ admits an $ \mathcal{H} $-factor. A graph $ G $ is called an $ (\mathcal{H}, n) $-factor critical graph if for every $ N\subseteq V(G) $ with $ |N| = n $, $ G-N $ admits an $ \mathcal{H} $-factor. Let $ m $, $ n $ and $ k $ be three nonnegative integers with $ k\geq2 $, and write $ \mathcal{F} = \{P_2, C_3, P_5, \mathcal{T}(3)\} $ and $ \mathcal{H} = \{K_{1, 1}, K_{1, 2}, \cdots, K_{1, k}, \mathcal{T}(2k+1)\} $, where $ \mathcal{T}(3) $ and $ \mathcal{T}(2k+1) $ are two special families of trees. In this article, we verify that (i) a $ (2m+1) $-connected graph $ G $ is an $ (\mathcal{F}, m) $-factor deleted graph if its binding number $ bind(G)\geq\frac{4m+2}{2m+3} $; (ii) an $ (n+2) $-connected graph $ G $ is an $ (\mathcal{F}, n) $-factor critical graph if its binding number $ bind(G)\geq\frac{2+n}{3} $; (iii) a $ (2m+1) $-connected graph $ G $ is an $ (\mathcal{H}, m) $-factor deleted graph if its binding number $ bind(G)\geq\frac{2}{2k-1} $; (iv) an $ (n+2) $-connected graph $ G $ is an $ (\mathcal{H}, n) $-factor critical graph if its binding number $ bind(G)\geq\frac{2+n}{2k+1} $.</p></abstract>

2019 ◽  
Vol 53 (3) ◽  
pp. 723-730 ◽  
Author(s):  
Sizhong Zhou

For a set ℋ of connected graphs, a spanning subgraph H of a graph G is called an ℋ-factor of G if every component of H is isomorphic to a member ofℋ. An H-factor is also referred as a component factor. If each component of H is a star (resp. path), H is called a star (resp. path) factor. By a P≥ k-factor (k positive integer) we mean a path factor in which each component path has at least k vertices (i.e. it has length at least k − 1). A graph G is called a P≥ k-factor covered graph, if for each edge e of G, there is a P≥ k-factor covering e. In this paper, we prove that (1) a graph G has a {K1,1,K1,2, … ,K1,k}-factor if and only if bind(G) ≥ 1/k, where k ≥ 2 is an integer; (2) a connected graph G is a P≥ 2-factor covered graph if bind(G) > 2/3; (3) a connected graph G is a P≥ 3-factor covered graph if bind(G) ≥ 3/2. Furthermore, it is shown that the results in this paper are best possible in some sense.


2010 ◽  
Vol 53 (2) ◽  
pp. 378-384
Author(s):  
Sizhong Zhou

AbstractLet G be a graph of order p, let a, b, and n be nonnegative integers with 1 ≤ a < b, and let g and f be two integer-valued functions defined on V(G) such that a ≤ g(x) < f (x) ≤ b for all x ∈ V(G). A (g, f )-factor of graph G is a spanning subgraph F of G such that g(x) ≤ dF(x) ≤ f (x) for each x ∈ V(F). Then a graph G is called (g, f, n)-critical if after deleting any n vertices of G the remaining graph of G has a (g, f )-factor. The binding number bind(G) of G is the minimum value of |NG(X)|/|X| taken over all non-empty subsets X of V(G) such that NG(X) ≠ V(G). In this paper, it is proved that G is a (g, f, n)-critical graph ifFurthermore, it is shown that this result is best possible in some sense.


2020 ◽  
Vol 30 (03) ◽  
pp. 2040008
Author(s):  
Chengfu Qin ◽  
Weihua Yang

Yoshimi Egawa [8] showed that a 5-connected graph G admits at most [Formula: see text] 5-shredders. In this paper we shown that a contraction-critical 5-connected graph G admits at most [Formula: see text] 5-shredders. Further we show that, for every contraction-critical 5-connected graph G, there is a contraction critical 5-connected graph [Formula: see text] such that G is a spanning subgraph of [Formula: see text] and [Formula: see text] admits at most [Formula: see text] 5-shredders.


2016 ◽  
Vol 09 (02) ◽  
pp. 1650041
Author(s):  
M. R. Chithra ◽  
A. Vijayakumar

Let [Formula: see text] be a family of connected graphs. A spanning subgraph [Formula: see text] of [Formula: see text] is called an [Formula: see text]-factor (component factor) of [Formula: see text] if each component of [Formula: see text] is in [Formula: see text]. In this paper, we study the component factors of the Cartesian product of graphs. Here, we take [Formula: see text] and show that every connected graph [Formula: see text] has a [Formula: see text]-factor where [Formula: see text] and [Formula: see text] is the maximum degree of an induced subgraph [Formula: see text] in [Formula: see text] or [Formula: see text]. Also, we characterize graphs [Formula: see text] having a [Formula: see text]-factor.


2007 ◽  
Vol 76 (2) ◽  
pp. 307-314 ◽  
Author(s):  
Sizhong Zhou ◽  
Jiashang Jiang

Let G be a graph of order n, and let a, b, k be nonnegative integers with 1 ≤ a < b. An [a, b]-factor of graph G is defined as a spanning subgraph F of G such that a ≤ dF(x) ≤ b for each x ϵ V (F). Then a graph G is called an (a, b, k)-critical graph if after deleting any k vertices of G the remaining graph of G has an [a, b]-factor. In this paper, it is proved that G is an (a, b, k)-critical graph if the binding number and Furthermore, it is showed that the result in this paper is best possible in some sense.


2019 ◽  
Vol 17 (1) ◽  
pp. 1490-1502 ◽  
Author(s):  
Jia-Bao Liu ◽  
Muhammad Javaid ◽  
Mohsin Raza ◽  
Naeem Saleem

Abstract The second smallest eigenvalue of the Laplacian matrix of a graph (network) is called its algebraic connectivity which is used to diagnose Alzheimer’s disease, distinguish the group differences, measure the robustness, construct multiplex model, synchronize the stability, analyze the diffusion processes and find the connectivity of the graphs (networks). A connected graph containing two or three cycles is called a bicyclic graph if its number of edges is equal to its number of vertices plus one. In this paper, firstly the unique graph with a minimum algebraic connectivity is characterized in the class of connected graphs whose complements are bicyclic with exactly three cycles. Then, we find the unique graph of minimum algebraic connectivity in the class of connected graphs $\begin{array}{} {\it\Omega}^c_{n}={\it\Omega}^c_{1,n}\cup{\it\Omega}^c_{2,n}, \end{array}$ where $\begin{array}{} {\it\Omega}^c_{1,n} \end{array}$ and $\begin{array}{} {\it\Omega}^c_{2,n} \end{array}$ are classes of the connected graphs in which the complement of each graph of order n is a bicyclic graph with exactly two and three cycles, respectively.


2021 ◽  
Vol 66 (3) ◽  
pp. 3-7
Author(s):  
Anh Nguyen Thi Thuy ◽  
Duyen Le Thi

Let l ≥ 1, k ≥ 1 be two integers. Given an edge-coloured connected graph G. A path P in the graph G is called l-rainbow path if each subpath of length at most l + 1 is rainbow. The graph G is called (k, l)-rainbow connected if any two vertices in G are connected by at least k pairwise internally vertex-disjoint l-rainbow paths. The smallest number of colours needed in order to make G (k, l)-rainbow connected is called the (k, l)-rainbow connection number of G and denoted by rck,l(G). In this paper, we first focus to improve the upper bound of the (1, l)-rainbow connection number depending on the size of connected graphs. Using this result, we characterize all connected graphs having the large (1, 2)-rainbow connection number. Moreover, we also determine the (1, l)-rainbow connection number in a connected graph G containing a sequence of cut-edges.


10.37236/1211 ◽  
1995 ◽  
Vol 2 (1) ◽  
Author(s):  
Carl Droms ◽  
Brigitte Servatius ◽  
Herman Servatius

We expand on Tutte's theory of $3$-blocks for $2$-connected graphs, generalizing it to apply to infinite, locally finite graphs, and giving necessary and sufficient conditions for a labeled tree to be the $3$-block tree of a $2$-connected graph.


2018 ◽  
Vol 12 (2) ◽  
pp. 297-317
Author(s):  
Encarnación Abajo ◽  
Rocío Casablanca ◽  
Ana Diánez ◽  
Pedro García-Vázquez

Let G be a connected graph with n vertices and let k be an integer such that 2 ? k ? n. The generalized connectivity kk(G) of G is the greatest positive integer l for which G contains at least l internally disjoint trees connecting S for any set S ? V (G) of k vertices. We focus on the generalized connectivity of the strong product G1 _ G2 of connected graphs G1 and G2 with at least three vertices and girth at least five, and we prove the sharp bound k3(G1 _ G2) ? k3(G1)_3(G2) + k3(G1) + k3(G2)-1.


2019 ◽  
Vol 19 (04) ◽  
pp. 2050068
Author(s):  
Hezan Huang ◽  
Bo Zhou

The distance spectral radius of a connected graph is the largest eigenvalue of its distance matrix. For integers [Formula: see text] and [Formula: see text] with [Formula: see text], we prove that among the connected graphs on [Formula: see text] vertices of given maximum degree [Formula: see text] with at least one cycle, the graph [Formula: see text] uniquely maximizes the distance spectral radius, where [Formula: see text] is the graph obtained from the disjoint star on [Formula: see text] vertices and path on [Formula: see text] vertices by adding two edges, one connecting the star center with a path end, and the other being a chord of the star.


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