English

Fair representation in the intersection of two matroids

Combinatorics 2017-01-06 v3

Abstract

For a simplicial complex C{\mathcal C} denote by β(C)\beta({\mathcal C}) the minimal number of edges from C{\mathcal C} needed to cover the ground set. If C{\mathcal C} is a matroid then for every partition A1,,AmA_1, \ldots, A_m of the ground set there exists a set SCS \in {\mathcal C} meeting each AiA_i in at least Aiβ(C)\frac{|A_i|}{\beta({\mathcal C})} elements. We conjecture that a slightly weaker result is true for the intersections of two matroids: if D=PQ{\mathcal D}={\mathcal P} \cap {\mathcal Q}, where P,Q{\mathcal P},{\mathcal Q} are matroids on the same ground set VV and β(P),β(P)k\beta({\mathcal P}), \beta({\mathcal P}) \le k, then for every partition A1,,AmA_1, \ldots, A_m of the ground set there exists a set SDS \in {\mathcal D} meeting each AiA_i in at least (1k1V)Ai1(\frac{1}{k}-\frac{1}{|V|})|A_i|-1 elements. We prove this for a partition into two sets.

Keywords

Cite

@article{arxiv.1612.07652,
  title  = {Fair representation in the intersection of two matroids},
  author = {Ron Aharoni and Eli Berger and Dani Kotlar and Ran Ziv},
  journal= {arXiv preprint arXiv:1612.07652},
  year   = {2017}
}
R2 v1 2026-06-22T17:32:30.624Z