2k-系整数可重集伴随等价图的计数

给出了由2k-系的整数组成的可重集的伴随等价图的个数问题,同时也给出了其补图的色等价图的个数.     

ω_(aδ)~ω∪bω_δ形图簇的伴随分解及其补图的色等价性

研究图的伴随分解及其补图的色等价性.采用伴随多项式的性质讨论图的伴随分解式,通过图的伴随分解式确定其补图的色性.证明了形图簇的伴随多项式的分解定理,从上述定理得到了这类图簇的补图的色等价性.结论通过图的伴随分解研究其补图的色等价性,是有效的途径与方法,从图的伴随分解式容易看出其补图的色等价图的结构规律.     

构造色等价图的几种新方法

给出了构造伴随等价图的几种新方法，因而也给出了构造色等价图的几种新方法。     

Φ~S-型图簇的伴随分解及其色性分析

运用图的伴随多项式的性质,讨论了图簇ΦS((kn+1)σ,nσ)∪2kSσ的伴随多项式的因式分解定理,进而证明了它们的补图的色等价性.     

具有色多项式∑n＋2／k[k n＋2—k]（λ）k＋1的图

本文讨论了色项式为∑/k≤n 2(n 2)/k[k n 2-k](λ）k 1的图的结构,给出了具有这种色多项式的全部色等价图。     

S~(GS*)类图簇的伴随多项式的因式分解及其色性

通过研究SGS*类图簇的伴随多项式的因式分解,证明了这类图簇的补图的色等价图的结构特征.     

Y(2,2,λ)形图的伴随多项式的分解及其补图的色等价性

构造了两类图簇Y(2,2,λ)∪K1(m为奇数)和Y(2,2,λ)∪EGδ(m为偶数).运用图的伴随多项式,讨论了这两类图簇的伴随多项式的因式分解式,(m=2k-1q-1,λk=(2kq-1)+2k-1qδ),研究了图簇Y(2,2,λk)∪(k-1)K1和Y(2,2,λk)的伴随多项式的因式分解式,进而证明了这些图的补图的色等价性.     

图的伴随多项式基于挖补定理的因式分解及其色性分析

通过研究H_t~Γ及H_t~L类图簇的伴随多项式的因式分解,证明了两类图的补图的色等价图的结构性质和非色唯一性.     

S~s一类图簇的伴随多项式的因式分解及色性分析

通过研究图的伴随多项式的因式分解 ,给出了证明非色唯一图的一种新方法 ,并且得到了色等价图的一些结构特性 .     

若干图簇的伴随多项式的因式分解及色性分析

我们通过研究图的伴随多项式的因式分解,给出了证明非色唯一图的一种新方法,同时得到若干图簇的色等价图的结构定理.     

Jump number of dags having Dilworth number 2

The jump number, denoted by σ, of a directed acyclic graph (dag) G, is the minimum number of arcs that have to be added to G such that the resulting graph is still acyclic and has a hamiltonian path.We study here the particular class of dags having an induced partial order of width 2, and give a characterization of such graphs with σ(G)=i. This yields immediately a polynomial algorithm to compute the jump number in this particular class.     

Euclidean number fields 2

The Mathematical Intelligencer -     

The number of 2-sat functions

Our aim in this paper is to address the following question: of the 2^{2 n} Boolean functions onn variables, how many are expressible as 2-SAT formulae? In other words, we wish to count the number of different instances of 2-SAT, counting two instances as equivalent if they have the same set of satisfying assignments. Viewed geometrically, we are asking for the number of subsets of then-dimensional discrete cube that are unions of (n-2)-dimensional subcubes.There is a trivial upper bound of 2^4(n/2), the number of 2-SAT formulae. There is also an obvious lower bound of 2^(n/2), corresponding to the monotone 2-SAT formulae. Our main result is that, rather surprisingly, this lower bound gives the correct speed: the number of 2-SAT functions is 2^(1+0(1)) n ^{2 2}.     

On the 2-part of the class number of imaginary quadratic number fields

We employ a type number formula from the theory of quaternion algebras to gain information on the 2-part of the class numbers of imaginary quadratic number fields whose discriminants are divisible by three or fewer prime numbers.     

2-Domination number of generalized Petersen graphs

Let \(G=(V,E)\) be a graph. A subset \(S\subseteq V\) is a k-dominating set of G if each vertex in \(V-S\) is adjacent to at least k vertices in S. The k-domination number of G is the cardinality of the smallest k-dominating set of G. In this paper, we shall prove that the 2-domination number of generalized Petersen graphs \(P(5k+1, 2)\) and \(P(5k+2, 2)\), for \(k>0\), is \(4k+2\) and \(4k+3\), respectively. This proves two conjectures due to Cheng (Ph.D. thesis, National Chiao Tung University, 2013). Moreover, we determine the exact 2-domination number of generalized Petersen graphs P(2k, k) and \(P(5k+4,3)\). Furthermore, we give a good lower and upper bounds on the 2-domination number of generalized Petersen graphs \(P(5k+1, 3), P(5k+2,3)\) and \(P(5k+3, 3).\)     

On tactical decompositions of class number 2

In this article we consider tactical decompositions of class number 2 of symmetric designs. Our main result says that if the orders are prime, then the only decompositions are of affine type. Moreover, we study symmetric decompositions of finite projective planes and show that, except in some cases, they are related to Baer subplanes, unitals, or 2 - ((m ² - m + 1)m, m, 1)designs.     

Imaginary quadratic fields of class number 2

A conjecture concerning linear forms in the logarithms of algebraic numbers is made. It is shown that this conjecture allows an effective determination of all imaginary quadratic fields of class number 2.     

Characterization of graphs with hall number 2

Hall's condition is a simple requirement that a graph G and list assignment L must satisfy if G is to have a proper L‐colouring. The Hall number of G is the smallest integer m such that whenever the lists on the vertices each has size at least m and Hall's condition is satisfied a proper L‐colouring exists. Hilton and P.D. Johnson introduced the parameter and showed that a graph has Hall number 1 if and only if every block is a clique. In this paper we give a forbidden‐induced‐subgraph characterization of graphs with Hall number 2. © 2003 Wiley Periodicals, Inc. J Graph Theory 45: 81–100, 2004     

Graded filtrations and ideals of reduction number 2

In this paper, we give a way to construct graded filtrations of graded modules. We then apply it to the Sally module, which describes a correction term of the Hilbert function. As a result, we obtain the inequality of the Hilbert coefficients for ideals of reduction number 2 or 3.