English

Sumsets of sequences in abelian groups and flags in field extensions

Combinatorics 2022-07-22 v1 Number Theory

Abstract

For a finite abelian group GG with subsets AA and BB, the sumset ABAB is {abaA,bB}\{ab \mid a\in A, b \in B\}. A fundamental problem in additive combinatorics is to find a lower bound for the cardinality of ABAB in terms of the cardinalities of AA and BB. This article addresses the analogous problem for sequences in abelian groups and flags in field extensions. For a positive integer nn, let [n][n] denote the set {0,,n1}\{0,\dots,n-1\}. To a finite abelian group GG of cardinality nn and an ordering G={1=v0,,vn1}G = \{1=v_0,\dots,v_{n-1}\}, associate the function T ⁣:[n]×[n][n]T \colon [n] \times [n] \rightarrow [n] defined by T(i,j)=min{k[n]{v0,,vi}{v0,,vj}{v0,,vk}}. T(i,j) = \min\big\{k \in [n] \mid \{v_0,\dots,v_i\}\{v_0,\dots,v_j\} \subseteq \{v_0,\dots,v_k\}\big\}. Under the natural partial ordering, what functions TT are minimal as {1=v0,,vn1}\{1=v_0,\dots,v_{n-1}\} ranges across orderings of finite abelian groups of cardinality nn? We also ask the analogous question for degree nn field extensions. We explicitly classify all minimal TT when n<18n < 18, nn is a prime power, or nn is a product of 22 distinct primes. When nn is not as above, we explicitly construct orderings of abelian groups whose associated function TT is not contained in the above classification. We also associate to orderings a polyhedron encoding the data of TT.

Keywords

Cite

@article{arxiv.2207.10507,
  title  = {Sumsets of sequences in abelian groups and flags in field extensions},
  author = {Sameera Vemulapalli},
  journal= {arXiv preprint arXiv:2207.10507},
  year   = {2022}
}

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