A weakly pandiagonal Latin square of order n over the number set {0, 1, . . . , n-1} is a Latin square having the property that the sum of the n numbers in each of 2n diagonals is the same. In this paper, we shall prove that a pair of orthogonal weakly pandiagonal Latin squares of order n exists if and only if n ≡ 0, 1, 3 （mod 4） and n≠3.
Difference systems of sets (DSSs) are combinatorial configurations which were introduced in 1971 by Levenstein for the construction of codes for synchronization. In this paper, we present two kinds of constructions of difference systems of sets by using disjoint difference families and a special type of difference sets, respectively. As a consequence, new infinite classes of optimal DSSs are obtained.
Detecting arrays were proposed by Colbourn and McClary in 2008, which are of interest in generating software test suites to cover all t-sets of component interactions and detect interaction faults in component-based systems. So far, optimality and constructions of detecting arrays have not been studied systematically. Indeed, no useful benchmark to measure the optimality of detecting arrays has previously been given, and only some sporadic examples of optimal detecting arrays have been found. This paper tries to take the first step by presenting a lower bound on the size of detecting arrays and some methods of constructing optimal detecting arrays. A number of infinite series of optimal detecting arrays are then obtained.
Orthogonal arrays (OAs), mixed level or fixed level (asymmetric or symmetric), are useful in the design of various experiments. They are also a fundamental tool in the construction of various combinatorial configurations. In this paper, we establish a general "expansive replacement method" for constructing mixedlevel OAs of an arbitrary strength. As a consequence, a positive answer to the question about orthogonal arrays posed by Hedayat, Sloane and Stufken is given. Some series of mixed level OAs of strength ≥3 are produced.
A t-hyperwheel(t≥3) of length l(or W l(t) for brevity) is a t-uniform hypergraph(V,E) ,where E = {e1,e2,. . .,el} and v1,v2,. . .,vl are distinct vertices of V = il=1 ei such that for i = 1,. . .,l,vi,vi+1 ∈ ei and ei ∩ ej = P,j ∈/{i-1,i,i + 1},where the operation on the subscripts is modulo l and P is a vertex of V which is different from vi,1 i l. In this paper,we investigate the maximum packing problem of MPλ(3,W 4( 3) ,v) . Finally,the packing number Dλ(3,W 4( 3) ,v) is determined for any positive integers v 5 and λ.
WU Yan & CHANG YanXun Institute of Mathematics,Beijing Jiaotong University,Beijing 100044,China
A near generalized balanced tournament design, or an NGBTD(k,m) in short, is a (km+1,k,k-1)-BIBD defined on a (km+1)-set V . Its blocks can be arranged into an m×(km+1) array in such a way that (1) the blocks in every column of the array form a partial parallel class partitioning V\{x} for some point x, and (2) every element of V is contained in precise k cells of each row. In this paper, we completely solve the existence of NGBTD(4,m) and almost completely solve the existence of NGBTD(5,m) with four exceptions.
SHAN XiuLing1, 2 1 Department of Mathematics, Beijing Jiaotong University, Beijing 100044, China 2 College of Mathematics and Information Science, Hebei Normal University, Shijiazhuang 050016, China
A directed triple system of order v with index λ, briefly by DTS（v,λ）, is a pair （X, B） where X is a v-set and B is a collection of transitive triples （blocks） on X such that every ordered pair of X belongs to λ blocks of B. A simple DTS（v, λ） is a DTS（v, λ） without repeated blocks. A simple DTS（v, ）,） is called pure and denoted by PDTS（v, λ） if （x, y, z） ∈ B implies （z, y, x）, （z, x, y）, （y, x, z）, （y, z, x）, （x, z, y） B. A large set of disjoint PDTS（v, λ）, denoted by LPDTS（v, λ）, is a collection of 3（v - 2）/λ disjoint pure directed triple systems on X. In this paper, some results about the existence for LPDTS（v, λ） are presented. Especially, we determine the spectrum of LPDTS（v, 2）.
Abstract A t-hyperwhesl （t 〉 3） of length l （or Wz（t） for brevity） is a t-uniform hypergraph （V, E）, where t E= {e1,e2,...,el} and vl,v2,...,vt are distinct vertices of V = Ui=1 ei such that for i= 1,...,1, vi,vi＋1 ∈ei and ei ∩ ej = P, j ∈ {i - 1, i,i ＋ 1}, where the operation on the subscripts is modulo 1 and P is a vertex of V which is different from vi, 1 〈 i 〈 l. In this paper, the minimum covering problem of MCλ（3, W（3）,v） is investigated. Direct and recursive constructions on MCλ（3, W（3）,v） are presented. The covering number cλ（3, W4（3）, v） is finally determined for any positive integers v 〉 5 and A.
