从关联结构识别递归设计
Recognizing Recursive Designs from Their Incidence Structure
研究概述
这里的设计由互不相同、等大且至少含两个点的子集组成,这些子集称为区组;每个点属于同一个正数的区组。对于两种递归构造,我们仅从点与区组的隶属关系中恢复隐藏的分部,并确定所有保持区组的点置换,即自同构。这证明了 Amarra、Devillers 和 Praeger 的两个猜想,并分类了例外。隶属向量之间的整数关系还能在事先不知道参数时恢复单分划构造的输入设计。固定的有限构造步骤序列继承相应的群与同构结论。
原文摘要(英文)
Two recursive constructions of Amarra, Devillers and Praeger replace points by copies of a uniform design and produce natural wreath-product groups of automorphisms. We recover their defining partitions from the unlabelled incidence structures and determine the full automorphism groups, proving both of the authors' conjectures for arbitrary input 1-designs. The single-partition construction has exactly one exceptional family: two copies of a complete balanced bipartite graph. For the grid construction we also determine the full group in the two-row case, where independent permutations of the columns in each row enlarge the natural group. The proof uses the classical code generated by differences of block vectors. Its orthogonal space recovers fibers or grid columns; pair incidences handle the graph-input boundary. We compute the integer incidence quotients and all prime ranks of both constructions. The Smith normal form of the single-partition matrix gives parameter-free recovery of its input design. Fixed finite iterations inherit the group and isomorphism results.
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