English

Hypercube geodesics with few colour changes

Combinatorics 2026-05-29 v3

Abstract

What is the maximum, over all 2-colourings of the edges of the nn-dimensional hypercube QnQ_n, of the minimal number of times a path between a vertex vv and its antipode vˉ\bar{v} changes colour? A conjecture of Norine, in a form due to Feder and Subi, states that this maximum should be 1. The previous best-known upper bound on the number of colour changes was (516+o(1))n(\tfrac{5}{16} + o(1))n due to Kirchweger, Peitl, Subercaseaux, and Szeider. We improve this bound and answer a question of Leader and Long by finding a geodesic path with at most (π2+o(1))n(\tfrac{\pi}{2} + o(1))\sqrt{n} colour changes. In fact, we show that this is the expected number of colour changes for a uniformly random start vertex. This is optimal (up to the constant) when the start vertex is chosen uniformly at random.

Keywords

Cite

@article{arxiv.2605.20184,
  title  = {Hypercube geodesics with few colour changes},
  author = {Lawrence Hollom},
  journal= {arXiv preprint arXiv:2605.20184},
  year   = {2026}
}

Comments

8 pages, 1 figure