一个指标为3的可迁三元系DTS(v,3)是一个对子(X,B)(其中X为一个v元集,B为X中可迁三元组(称作区组)的集合),满足X的每个有序对都恰包含于B中的3个区组。设(X,B)是一个没有重复区组的DTS(v,3),如果(x,y,z)∈B,必有(z,y,x),(z,x,y),(y,x,z),(y,z,x),(x,z,y)埸B,则称(X,B)是单纯的,记为PDTS(v,3)。不相交PDTS(v,3)大集记为LPDTS(v,3),是一个集合{(X,Bi)}i,其中每个(X,Bi)都是PDTS(v,3),并且∪iBi构成X中所有可迁三元组的一个划分。本文给出了LPDTS(v,3)的一种三倍构造方法,得到了其存在的一个无穷类:对于任意正整数v,v≡8,14(mod18),存在LPDTS(v,3)。结论对构作常重码具有重要的参考价值和理论意义。
There are two kinds of oriented triples on X:the cyclic triple and the transitive triple.A cyclic triple on X is a set of three ordered pairs(x,y),(y,z) and(z,x) of X,which is denoted by x,y,z(or y,z,x,or z,x,y),and a transitive triple on X is a set of three ordered pairs(x,y),(y,z) and(x,z) of X,which is denoted by(x,y,z).An oriented triple system of order v with index λ is a pair(X,B)where X is a v-set and B is a collection of oriented triples on X,called blocks,such that every ordered pair of X belongs to exactly λ blocks of B.If B consists of transitive(or cyclic) triples only,the system is called a directed triple system(or Mendelsohn triple system) of order v with index λ and denoted by DTS(v,λ)(or MTS(v,λ)).If B contains both cyclic triples and transitive triples,the system is called a hybrid triple system of order v with index λ and denoted by HTS(v,λ).A triple system is called simple if there are no repeated blocks in B.A simple DTS(v,λ) 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)s,denoted by LPDTS(v,λ),is a collection of {(X,Bi)}i where each(X,Bi) is a PDTS(v,λ) and ∪iBi is a partition of all transitive triples on X.In this paper,a tripling construction for LPDTS(v,3) is presented,and one infinite family for the existence of LPDTS(v,3) is obtained:for any positive integers v,v≡8,14(mod18),there exists an LPDTS(v,3).