RESEARCH ANNOUNCEMENTS——Strong Discreteness of Subgroups of SL（2, Гn）

As in [1,6], let Гn be the n-dimensional Clifford group, i.e., the set of all elements in n-dimensional Clifford algebra An, which can be expressed as a finite product of non-zero-vertors and SL(2, Гn) denote the group of n-dimensional Clifford matrices A=(α b c d)which satisfy:     

Nonsingularity on Level—2（r1,r2）—circulant Matrices of Type（m,n）

ＮｏｎｓｉｎｇｕｌａｒｉｔｙｏｎＬｅｖｅｌ－２（ｒ_１，ｒ_２）－ｃｉｒｃｕｌａｎｔＭａｔｒｉｃｅｓｏｆＴｙｐｅ（ｍ，ｎ）ＪｉａｎｇＺｈａｏｌｉｎ（江兆林）（Ｄｅｐｔ．ｏｆＭａｔｈ．，ＬｉｎｙｉＴｅａｃｈｅｒ＇ｓＣｏｌｌｅｇｅ，Ｓｈａｎｄｏｎｇ，Ｌｉｎ...     

Balanced path decomposition of λ K n,n and λ K n,n *

Let P _k denote a path with k edges and λ K _n,n denote the λ-fold complete bipartite graph with both parts of size n. In this paper, we obtain the necessary and sufficient conditions for λ K _n,n to have a balanced P _k -decomposition. We also obtain the directed version of this result.     

（n,n2,…nk）型（r1,r2,…rk）—循环矩阵非异性的一个判定

当|r1|=|r2|=…=|rk|=1时,本文给出了（n1,n2,…,nk）型k重（r1,r2,…rk)－循环矩阵非异性的一个判定方法。     

二阶矩阵的n次方和n次方根

利用Chebyshev多项式讨论了二阶矩阵的n次方的各元素的表达式和其n次方根的存在条件.     

（n1,n2）型二重（r1,r2）——循环矩阵及有关算法的计算复杂性

1引言循环矩阵是一类很重要的特殊矩阵，在实中有着广泛的应用，如在理论物理、固态物理、数字图像处理、自回归滤波器设计、计算机时序分析以及石油勘探等许多大型计算中经常要遇到这类矩阵，因而近年来对这类矩阵的特性及有关快速算法的研究，引起人们的普遍重视。     

The Associated Matrices of Ap,n,4p—5 Polyhedra and their Admissible Operations

In this paper we describe the decomposition problem of a special kind of Ap,n,4p-5 polyhedra by using the associated matrices and their admissible operations.     

（n1,n2,...nK）型k重循环矩阵逆矩阵的特殊求法

本文利用一个特殊k重循环矩阵Fn1n2…nk的性质，给出了［1～3］中研究的（n1，n2，…，nk）型k重循环矩阵逆矩阵的一种特殊求法．     

二元码M_q(n,d,k)的检错性和纠错性

二元码Mq(n,d,k)是一个非适应性分组测试(NGT)算法的数学模型,是一个d-disjunct矩阵.二元码的汉明距离(Hamming)决定着码的检错性和纠错性,通过计算二元码Mq(n,d,k)的汉明距离,得到了它的检错性和纠错性.     

（n1,n2）型二重（r1,r2）—循环矩阵逆矩阵的插值求法

本文用插值法给出n1n2阶（n1，n2）型二重（r1，r2）－循环矩阵逆矩阵计算公式．     

基于矩阵M_q(n,k,d)的可纠错非适应性群测

二元矩阵M_q(n,k,d)是一个非适应性分组测试(NGT)算法的数学模型,它是一个d-析取矩阵.在矩阵M_q(n,k,d)的基础上研究它的子矩阵M_q(n.k,d,z)的检纠错性质.     

$(m,n)$-Igusa-Todorov 代数,IT-维数和三角矩阵代数

设$T$, $U$是两个Artin代数, $_U M_T$是$U$-$T$-双模.本文得到了三角矩阵代数$\Lambda=\left({\smallmatrix T&0\\ M&U \endsmallmatrix}\right)$是$(m,n)$-Igusa-Todorov的一个充要条件.我们还研究了$\Lambda$的IT维数.更具体地说,事实证明$$\max\{\ITdim T, \ITdim U\}\leqslant\ITdim \Lambda\leqslant\min\{\max\{\gldim T,\ITdim U\},\max\{\gldim U,\ITdim T\}\}.$$     

The Spectrum of （gv,g, 3, λ）-dDF in Zgv

In this paper, several recursive constructions for directed difference family and perfect directed difference family are presented by means of difference matrix and incomplete difference matrix. Finally the necessary and sufficient conditions for the existence of a （gv, g, 3, λ）-directed difference family in Zgv are established. As a consequence, the necessary and sufficient conditions for the existence of a cyclic directed group divisible design with block size three and type gv are obtained.     

2-Arc-transitive cyclic covers of K n,n −nK 2

Du et al. (in J. Comb. Theory B 74:276–290, 1998 and J. Comb. Theory B 93:73–93, 2005), classified regular covers of complete graph whose fiber-preserving automorphism group acts 2-arc-transitively, and whose covering transformation group is either cyclic or isomorphic to $\mathbb{Z}_{p}^{2}$ or $\mathbb{Z}_{p}^{3}$ with p a prime. In this paper, a complete classification is achieved of all the regular covers of bipartite complete graphs minus a matching K _n,n ?nK ₂ with cyclic covering transformation groups, whose fiber-preserving automorphism groups act 2-arc-transitively.     

On the Self-adjointness of the Product Operators of Two ruth-Order Differential Operators on [0, ＋∞）

In the present paper, the self-adjointness of the product of two mth-order differential operators on [0, ∞) is studied. By means of the construction theory of self-adjoint operators and matrix computation, we obtain a sufficient and necessary condition to ensure that the product operator is self-adjoint, which extends the results in the second order case.