共查询到18条相似文献,搜索用时 125 毫秒
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图G是一个简单无向图,G~σ是图G在定向σ下的定向图,G被称作G~σ的基础图.定向图G~σ的斜Randi6矩阵是实对称n×n矩阵R_s(G~σ)=[(r_s)_(ij)].如果(v_i,v_j)是G~σ的弧,那么(r_s)_(ij)=(d_id_j)~(-1/2)且(r_s)_(ji)=(d_id_j)~(-1/2),否则(r_s)_(ij)=(r_s)_(ji)=0.定向图G~σ的斜Randi能量RE_s(G~σ)是指R_s(G~σ)的所有特征值的绝对值的和.首先刻画了定向图G~σ的斜Randi矩阵R_s(G~σ)的特征多项式的系数.然后给出了定向图G~σ的斜Randi能量RE_s(G~σ)的积分表达式.之后给出了RE_s(G~σ)的上界.最后计算了定向圈的斜Randi能量RE_s(G~σ). 相似文献
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给定图$G$,对图$G$的每条边确定一个方向,称为$G$的定向图$G^\sigma$, $G$称为$G^\sigma$的基础图. $G^\sigma$的斜邻接矩阵$S(G^\sigma)$是反对称矩阵,其特征值是0或纯虚数. $S(G^\sigma)$所有特征值的$k$次幂之和称为$G^\sigma$的$k$阶斜谱矩,其中$k$是非负整数.斜谱矩序列可用于对图进行排序.本文主要研究定向树和定向单圈图的斜谱矩,并对这两类图的斜谱矩序列依照字典序进行排序.首先确定了直径为$d$的树作为基础图的所有定向树中,斜谱矩序最大的$2\lfloor\frac{d}{4}\rfloor$个图; 然后确定以围长为$g$的单圈图作为基础图的所有定向单圈图中, 斜谱矩序最大的$2\lfloor\frac{g}{4}\rfloor+1$个图. 相似文献
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设G是一个无向图.如果对G的任一(某个)定向图G,G的斜邻接矩阵S(G)的每一个特征值λ,其倒数1/λ同样也是S(G)的特征值,且重数与λ相同,就称G是具有强迫(允许)斜特征值互逆性质.本文确定了所有具有强迫(允许)斜特征值互逆性质的单圈图. 相似文献
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《高校应用数学学报(A辑)》2021,(2)
设A(G)和D(G)分别表示n阶图G的邻接矩阵和度对角矩阵,对于任意实数α∈[0, 1],图G的A_(a~-)矩阵被定义为Aα(G)=αD(G)+(1-α)A(G),它是图的邻接矩阵和无符号拉普拉斯矩阵的共同推广,其最大特征根称为图G的A_(a~-)谱半径.单圈图与双圈图补图的A_(a~-)谱半径的上界被分别确定,相应的极图被完全刻画. 相似文献
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《应用数学与计算数学学报》2017,(1)
令G为简单无向图,给图G的每条边赋予一个方向,得到的有向图记为G~σ.有向图G~σ的斜能量ε_s(G~σ)定义为G~σ的斜邻接矩阵特征值的绝对值之和.运用奇异值不等式,得到了有向图斜能量和去边后所得有向子图斜能量之间的若干性质. 相似文献
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The Wiener index of a connected graph G is defined to be the sum of all distances of pairs of distinct vertices of G. Yu and Feng (Ars Comb 94:361–369, 2010) determined the unique graph having the largest Wiener index among all unicyclic graphs given girth. In the article we first give two new graphic transformations. Then with them we determine the graphs having the second largest Wiener index among all unicyclic graphs given girth and we also determine the graphs having the largest Wiener index among all unicyclic graphs given maximum degree. 相似文献
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In this paper, the effects on the signless Laplacian spectral radius of a graph are studied when some operations, such as
edge moving, edge subdividing, are applied to the graph. Moreover, the largest signless Laplacian spectral radius among the
all unicyclic graphs with n vertices and k pendant vertices is identified. Furthermore, we determine the graphs with the largest
Laplacian spectral radii among the all unicyclic graphs and bicyclic graphs with n vertices and k pendant vertices, respectively. 相似文献
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A mixed graph means a graph containing both oriented edges and undirected edges. The nullity of the Hermitian-adjacency matrix of a mixed graph G, denoted by ηH(G),is referred to as the multiplicity of the eigenvalue zero. In this paper, for a mixed unicyclic graph G with given order and matching number, we give a formula on ηH(G), which combines the cases of undirected and oriented unicyclic graphs and also corrects an error in Theorem 4.2 of [Xueliang LI, Guihai YU. The skew-rank of oriented graphs. Sci. Sin. Math., 2015, 45:93-104(in Chinese)]. In addition, we characterize all the n-vertex mixed graphs with nullity n-3, which are determined by the spectrum of their Hermitian-adjacency matrices. 相似文献
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Yi-Zheng Fan 《Linear and Multilinear Algebra》2013,61(2):97-113
Using the result on Fiedler vectors of a simple graph, we obtain a property on the structure of the eigenvectors of a nonsingular unicyclic mixed graph corresponding to its least eigenvalue. With the property, we get some results on minimizing and maximizing the least eigenvalue over all nonsingular unicyclic mixed graphs on n vertices with fixed girth. In particular, the graphs which minimize and maximize, respectively, the least eigenvalue are given over all such graphs with girth 3. 相似文献
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We consider the class of unicyclic graphs on n vertices with girth g, and over that class, we attempt to determine which graph maximizes the algebraic connectivity. When g is fixed, we show that there is an N such that for each n>N, the maximizing graph consists of a g cycle with n?g pendant vertices adjacent to a common vertex on the cycle. We also provide a bound on N. On the other hand, when g is large relative to n, we show that this graph does not maximize the algebraic connectivity, and we give a partial discussion of the nature of the maximizing graph in that situation. 相似文献
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Let G be a graph with n vertices and ν(G) be the matching number of G. Let η(G) denote the nullity of G (the multiplicity of the eigenvalue zero of G). It is well known that if G is a tree, then η(G)=n-2ν(G). Tan and Liu [X. Tan, B. Liu, On the nullity of unicyclic graphs, Linear Alg. Appl. 408 (2005) 212-220] proved that the nullity set of all unicyclic graphs with n vertices is {0,1,…,n-4} and characterized the unicyclic graphs with η(G)=n-4. In this paper, we characterize the unicyclic graphs with η(G)=n-5, and we prove that if G is a unicyclic graph, then η(G) equals , or n-2ν(G)+2. We also give a characterization of these three types of graphs. Furthermore, we determine the unicyclic graphs G with η(G)=0, which answers affirmatively an open problem by Tan and Liu. 相似文献
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A graph is called unicyclic if it owns only one cycle. A matching M is called uniquely restricted in a graph G if it is the unique perfect matching of the subgraph induced by the vertices that M saturates. Clearly, μ r (G) ≤ μ(G), where μ r (G) denotes the size of a maximum uniquely restricted matching, while μ(G) equals the matching number of G. In this paper we study unicyclic bipartite graphs enjoying μ r (G) = μ(G). In particular, we characterize unicyclic bipartite graphs having only uniquely restricted maximum matchings. Finally, we present some polynomial time algorithms recognizing unicyclic bipartite graphs with (only) uniquely restricted maximum matchings. 相似文献
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Shuchao Li 《Linear algebra and its applications》2008,429(7):1619-1628
The nullity of a graph G, denoted by η(G), is the multiplicity of the eigenvalue zero in its spectrum. Cheng and Liu [B. Cheng, B. Liu, On the nullity of graphs, Electron. J. Linear Algebra 16 (2007) 60-67] characterized the extremal graphs attaining the upper bound n-2 and the second upper bound n-3. In this paper, as the continuance of it, we determine the extremal graphs with pendent vertices achieving the third upper bound n-4 and fourth upper bound n-5. We then proceed recursively to construct all graphs with pendent vertices which satisfy η(G)>0. Our results provide a unified approach to determine n-vertex unicyclic (respectively, bicyclic and tricyclic) graphs which achieve the maximal and second maximal nullity and characterize n-vertex extremal trees attaining the second and third maximal nullity. As a consequence we, respectively, determine the nullity sets of trees, unicyclic graphs, bicyclic graphs and tricyclic graphs on n vertices. 相似文献