GEOMETRIC CONSTRUCTION OF ASSOCIATION SCHEMES FROM DEGENERATE QUADRICS INPROJECTIVE SPACES PG(2v+δ+l-1,Fq) FOR q ODD

Let Fq be a finite field with q elements,where q is a power of an odd prime.In this paper,the authors consider a projective space PG(2v+δ+l,Fq) with dimension 2v+δ+l,partitioned into an affine space AG(2v+δ+l,Fq) of dimension 2v+δ+l and a hyperplane H=PG(2v+δ+l-1,Fq) of dimension 2v+δ+l-1 at infinity,where l≠0.The points of the hyperplane Hare next partitioned into four subsets.A pair of points a and b of the affine space is defined to belong to class i if the line ab meets the subset i of H.Finally,a family of four-class association schemes are constructed,and parameters are also computed.     

偶特征有限域上对称矩阵结合方案

设S(n,q)是偶特征有限域F_q上n×n对称矩阵所成的集合.令R_i={(X,Y)|X,Y∈S(n,q),rank(Y-X)=2i-1,2i},0≤i≤[(n+1)/2]采用矩阵方法,证明了Sym(n,q)={s(n,q),{R_i}_(0≤i≤)[(n+1)/2]}是[(n+1)/2]个结合类的P—多项式对称结合方案,而Sym(n,q)的结合关系的图Γ~((1))是正则的,并且它同构于交错矩阵结合方案.此外,又给出Sym(n,q)的自同构形式.     

特征为奇数的广义正交图的自同构

本文确定了特征为奇数的有限域F_q上广义正交图ГGO_(2v+δ)(q,m,S)的自同构,其中1mv.     

有限域上存在弱自对偶正规基的一个充要条件

对于将有限域上的自对偶基概念推广到了更一般的弱自对偶的情形,给出了有限域上存在这类正规基的一个充要条件设q为素数幂,E=Fqn为q元域F=Fq的n次扩张,N={αi=αq2| i=0,1,…,n-1}为E在F上的一组正规基.则存在c∈F*及r,0≤r≤n-1,使得β=cαr生成N的对偶基的充要条件是以下三者之一成立(1)q为偶数且n≠0(mod 4);(2)n与q均为奇数;(3)q为奇数,n为偶数,(-1)为F中的非平方元且r为奇数.     

有限域上存在弱自对偶正规基的一个充要条件

对于将有限域上的自对偶基概念推广到了更一般的弱自对偶的情形,给出了有限域上存在这类正规基的一个充妥条件:设q为素数幂,E=Fqn为q元域F=Fq的n次扩张,N={αi=αqi|i=0,1,…,n-1}为E在F上的一组正规基．则存在c∈F*及r,0≤r≤n-1,使得β=cαr生成N的对偶基的充要条件是以下三者之一成立: (1)q为偶数且n≠0(mod 4);(2) n与q均为奇数;(3)q为奇数,n为偶数,(-1)为F中的非平方元且r为奇数．     

轮图的广义Mycielski图的邻强边色数

设图 G(V,E)为简单图 ,V(Mn(G) ) |{ v0 1,v0 2 ,… ,v0 p;v11,v12 ,… ,v1p,… ,vn1,vn2 ,… ,vnp}E(Mn(G) ) =E(G)∪ { vijv(i+ 1) k|v0 jv0 k ∈ E(G) ,1≤ j,k≤ p ,i =0 ,1,… ,n - 1}称 Mn(G)为 G的 n广义 Mycielski图 ,n为自然数 .本文得到了轮的广义 Mycielski图的临强边色数 .     

奇异伪辛群的Carter子群

设 Fq是特征为 2的有限域 ,本文研究了 Fq上 2 ν+δ+t级奇异伪辛群 Ps2ν+δ+ t(Fq) (δ=1或 2 )的 Carter子群的存在性及结构 .得到的结果为 :若 q>2 ,Ps2ν+δ+ t(Fq)中不含 Carter子群 ,若 q=2 ,Ps2ν+δ+ t(Fq)的 Carter子群为它的 Sylow2 -子群的正规化子 .     

奇异辛空间上的一类Pooling设计的构作

利用有限域Fq上的奇异辛空间F(q2υ+l)构作一类具有高度纠错能力的Pooling设计,并且Pooling设计所包含的矩阵的级数是不依赖于数据集合中的阳性数据对象的个数.     

广义Mycielski图的邻强边色数和邻点可区别全色数的两个上界

对简单图G,|V(G)|=p,n是自然数,Mn(G)被称为图G的广义Mycielski图,如果V(Mn(G))={v01,v02,…,v0p;v11,v12,…,v1p;…;vn1,vn2,…,vnp},E(Mn(G))=E(G)∪{vijv(i+1)k|v0jv0k∈E(G),1≤j,k≤p,i=0,1,…,n-1}.文中针对简单图G与它的广义Mycielski图之间的关系,给出了G的广义Mycielski图的邻强边色数和邻点可区别全色数的两个上界.     

Automorphisms of generalized orthogonal graphs of characteristic 2

We determine the automorphism group of the generalized orthogonal graph GO2v＋δ（q, m, G） over Fq of characteristic 2, where 1 〈 m 〈 v.     

On Strongly Regular Graphs with k=2μ and Their Extensions

We obtain a convenient expression for the parameters of a strongly regular graph with k=2 in terms of the nonprincipal eigenvalues x and –y. It turns out in particular that such graphs are pseudogeometric for pG _x(2x,y–1). We prove that a strongly regular graph with parameters (35,16,6,8) is a quotient of the Johnson graph (8,4). We also find the parameters of strongly regular graphs in which the neighborhoods of vertices are pseudogeometric graphs for pG _x(2x,t),x3. In consequence, we establish that a connected graph in which the neighborhoods of vertices are pseudogeometric graphs for pG ₃(6,2) is isomorphic to the Taylor graph on 72 vertices or to the alternating form graph Alt(4,2) with parameters (64,35,18,20).     

Transitive bislim geometries of gonality 3, Part II: The group theoretic cases

We consider point-line geometries having three points on every line, having three lines through every point (bislim geometries), and containing triangles. We classify such geometries under the hypothesis of the existence of a collineation group acting transitively on the point set.     

一类半对称图的构造

称一个有限简单无向图X是半对称图,如果图X是正则的且边传递但非点传递.主要利用仿射几何构造了一类2p~n阶连通p~3。度的半对称图的无限族,其中p≥n≥8.     

The visibility graph of congruent discs is Hamiltonian

We show that the visibility graph of a set of disjoint congruent discs in is Hamiltonian, as long as the discs are not all supported by the same line. The proof is constructive, and leads to efficient algorithms for obtaining a Hamilton circuit.     

一类用仿射几何构造的半对称图

图X是一个有限简单无向图,如果图X是正则的且边传递但非点传递,则称X是半对称图.主要利用仿射几何构造了一类2p~n阶连通p~4度的半对称图的无限族,其中p≥n≥11.     

Antipodal distance-regular graphs of diameter four and five

An antipodal distance-regular graph of diameter four or five is a covering graph of a connected strongly regular graph. We give existence conditions for these graphs and show for some types of strongly regular graphs that no nontrivial covers exist. © 1999 John Wiley & Sons, Inc. J Combin Designs 7: 69–77, 1999     

2p~n阶连通p~2度的半对称图

称一个有限简单无向图X是半对称图,如果图X是正则的且边传递但非点传递.本文主要利用仿射几何构造了一类2p~n阶连通p~2度的半对称图的无限族,其中p≥n≥5.     

Separator theorems and Turán-type results for planar intersection graphs

We establish several geometric extensions of the Lipton-Tarjan separator theorem for planar graphs. For instance, we show that any collection C of Jordan curves in the plane with a total of m crossings has a partition into three parts C=S∪C₁∪C₂ such that , , and no element of C₁ has a point in common with any element of C₂. These results are used to obtain various properties of intersection patterns of geometric objects in the plane. In particular, we prove that if a graph G can be obtained as the intersection graph of n convex sets in the plane and it contains no complete bipartite graph Kt,t as a subgraph, then the number of edges of G cannot exceed ctn, for a suitable constant ct.     

GQ(4, 2)-extensions, strongly regular case

A strongly regular locallyGQ(4, 2)-graph is a graph with parameters either (126, 45, 12, 8) or (190, 45, 12, 10). The existence and the uniqueness of the corresponding locallyGQ(4, 2)-graph in the first case are well known. We prove that theGQ(4, 2)-hyperoval on ten vertices either is the Petersen graph, or is the Möbius 5-prism, or consists of two (2, 3)-subgraphs connected by three edges. We obtain homogeneousGQ(4, 2)-solutions with a strongly regular point graph; in particular, this implies the negative answer to the question of F. Buekenhout concerning the existence of a locallyGQ(4, 2)-graph with the parameters (190, 45, 12, 10).