图类aKa,a\βCP(b)中的整谱图

设图G是一个简单图,图G的补图记为G,如果G的谱都是整数.就称G是整谱图.鸡尾酒会图CP(n)=K2n-nK2(K2n是2n阶完全图)和完全二部图K…都是整谱图.确定了图类 aKa,a∪βCP中的所有的整谱图.     

图类■中的整谱图

设图G是一个简单图,图G的补图记为-G,如果G的谱都是整数,就称G是整谱图.鸡尾酒会图CP(n)=K2n-nK2(K2n是2n阶完全图)和完全图Ka都是整谱图[1].本文确定了图类■中的所有整谱图.     

图类￣(αKa∪βCP(b))中的整谱图

设图G是一个简单图,图G的补图记为(G),如果G的谱都是整数,就称G是整谱图.鸡尾酒会图CP(n)=K2n-nK2(K2n是2n阶完全图)和完全图Ka都是整谱图[1].本文确定了图类￣αKa∪βCP(b)中的所有整谱图.     

Q整图新类

对于一个简单图G, 方阵Q(G)=D(G)+A(G)称为G的无符号拉普拉斯矩阵,其中D(G)和A(G)分别为G的度对角矩阵和邻接矩阵. 一个图是Q整图是指该图的无符号拉普拉斯矩阵的特征值全部为整数.首先通过Stanic 得到的六个顶点数目较小的Q整图,构造出了六类具有无穷多个的非正则的Q整图. 进而,通过图的笛卡尔积运算得到了很多的Q整图类. 最后, 得到了一些正则的Q整图.     

梯子细分图L_n~*的排斥(下整)和数

(下整)和标号与排斥(下整)和标号是图的一种压缩表示.一个图G称为下整和图,若它同构于某个SQ+的下整和图.图Pn×K2称为梯子.本文给出了梯子细分图Ln*的定义,并确定了梯子细分图Ln*的排斥(下整)和数.     

图类αK_a∪βCP(b)中的一类特殊整谱图

图G是一个简单图,图G的补图记为G,如果G的谱完全由整数组成,就称G是整谱图.鸡尾酒会图CP(n)=K_(2n)-nK2(K_(2n是完全图)和完全图K_a都是整谱图.μ_1表示图类αK_a∪βCP(b)的一个主特征值,确定了当μ_1=2a并且a-1>2b-2时,图类αK_a∪βCP(b)中的所有的整谱图.     

新的Q整图类K_n~(-tk2)

在他人研究整图,Laplace整图和Seidel-整图的基础上,刻画了Q整图新类.对图类K-tk2n的无符号拉普拉斯特征多项式进行研究分析,应用矩阵的初等变换,给出了图类K-tk2n是Q整图的充分必要条件,得到了新的Q整图类K-tk2n及其Q谱.     

图类^-αKα∪βCP（b）中的整谱图

设图G是一个简单图,图G的补图记为^-G,如果G的谱都是整数,就称G是整谱图．鸡尾酒会图CP（n）=K2n-nK2（K2n是2n阶完全图）和完全图Kα都是整谱图．本文确定了图类^-αKα∪βCP（b）中的所有整谱图．     

图类αK_(α,α)UβCP(b)中的一类特殊整谱图

图G是一个简单,图G的补图记为G,如果G的谱完全由整数组成,就称G是整谱图,鸡尾酒会图CP (n)=K_(2n)-nK_2(K_(2n)是完全图)和完全二部图K_(a,a)都是整谱图.u_1表示图类αK_(α,α)UβCP(b)的一个主特征值,本文确图了当u_1=2b 1时,图类αK_(α,α)UβCP(b)中的所有的整谱图.     

f—因子覆盖的图

设G为图,f是定义在V(G)上的正整数值函数。称图G的支撑子图F为f-因子如果d_(?)(x)-f(x),x∈V(G).称图G是f-因子覆盖的如果G的每条边包含在一个f-因子中.本文给出了一个图是f-因子覆盖的图的充要条件,其结果推广了C.H.C.Little et al.[1]的1-因子覆盖定理。     

On Integral Graphs with Few Cycles

A graph is called integral if the spectrum of its adjacency matrix has only integer eigenvalues. In this paper, all integral graphs with at most two cycles (trees, unicyclic and bicyclic graphs) with no eigenvalue 0 are identified. Moreover, we give some results on unicyclic integral graphs with exactly one eigenvalue 0.     

Harary's conjectures on integral sum graphs

Let N denote the set of positive integers and Z denote all integers. The (integral) sum graph of a finite subset S N(Z) is the graph (S, E) with uv ε E if and only if u + v ε S. A graph G is said to be an (integral) sum graph if it is isomorphic to the (integral) sum graph of some S N(Z). The (integral) sum number of a given graph G is the smallest number of isolated nodes which when added to G result in an (integral) sum graph.

We show that the integral sum number of a complete graph with n 4 nodes equals 2n − 3, which proves a conjecture of Harary. And we disprove another conjecture of Harary by showing that there are infinitely many trees which are not caterpillars but are integral sum graphs.     

Integral trees of odd diameters

A graph is called integral if all eigenvalues of its adjacency matrix consist entirely of integers. Recently, Csikvári proved the existence of integral trees of any even diameter. In the odd case, integral trees have been constructed with diameter at most 7. In this article, we show that for every odd integer n>1, there are infinitely many integral trees of diameter n. © 2011 Wiley Periodicals, Inc. J Graph Theory     

Spanning trees of extended graphs

A generalization of the Prüfer coding of trees is given providing a natural correspondence between the set of codes of spanning trees of a graph and the set of codes of spanning trees of theextension of the graph. This correspondence prompts us to introduce and to investigate a notion ofthe spanning tree volume of a graph and provides a simple relation between the volumes of a graph and its extension (and in particular a simple relation between the spanning tree numbers of a graph and its uniform extension). These results can be used to obtain simple purely combinatorial proofs of many previous results obtained by the Matrix-tree theorem on the number of spanning trees of a graph. The results also make it possible to construct graphs with the maximal number of spanning trees in some classes of graphs.     

梯子细分图Ln＊的排斥（下整）和数

（下整）和标号与排斥（下整）和标号是图的一种压缩表示．一个图G称为下整和图,若它同构于某个S Q＋的下整和图．图Pn×K2称为梯子．本文给出了梯子细分图Ln＊的定义,并确定了梯子细分图Ln＊的排斥（下整）和数．     

Integral trees of diameter 6

A graph G is called integral if all eigenvalues of its adjacency matrix A(G) are integers. In this paper, the trees T(p,q)•T(r,m,t) and K_1,s•T(p,q)•T(r,m,t) of diameter 6 are defined. We determine their characteristic polynomials. We also obtain for the first time sufficient and conditions for them to be integral. To do so, we use number theory and apply a computer search. New families of integral trees of diameter 6 are presented. Some of these classes are infinite. They are different from those in the existing literature. We also prove that the problem of finding integral trees of diameter 6 is equivalent to the problem of solving some Diophantine equations. We give a positive answer to a question of Wang et al. [Families of integral trees with diameters 4, 6 and 8, Discrete Appl. Math. 136 (2004) 349-362].     

The swap graph of the finite soluble groups

A graph is reflexive if the second largest eigenvalue of its adjacency matrix is less than or equal to 2. In this paper, we characterize trees whose line graphs are reflexive. It turns out that these trees can be of arbitrary order—they can have either a unique vertex of arbitrary degree or pendant paths of arbitrary lengths, or both. Since the reflexive line graphs are Salem graphs, we also relate some of our results to the Salem (graph) numbers.     

Vector-valued fractal functions: Fractal dimension and fractional calculus

There are many research available on the study of a real-valued fractal interpolation function and fractal dimension of its graph. In this paper, our main focus is to study the dimensional results for a vector-valued fractal interpolation function and its Riemann–Liouville fractional integral. Here, we give some results which ensure that dimensional results for vector-valued functions are quite different from real-valued functions. We determine interesting bounds for the Hausdorff dimension of the graph of a vector-valued fractal interpolation function. We also obtain bounds for the Hausdorff dimension of the associated invariant measure supported on the graph of a vector-valued fractal interpolation function. Next, we discuss more efficient upper bound for the Hausdorff dimension of measure in terms of probability vector and contraction ratios. Furthermore, we determine some dimensional results for the graph of the Riemann–Liouville fractional integral of a vector-valued fractal interpolation function.     

Integral pentavalent Cayley graphs on abelian or dihedral groups

A graph is called integral, if all of its eigenvalues are integers. In this paper, we give some results about integral pentavalent Cayley graphs on abelian or dihedral groups.