English

A uniformness conjecture of the Kolakoski sequence, graph connectivity, and correlations

Combinatorics 2017-04-25 v3

Abstract

The Kolakoski sequence is the unique infinite sequence with values in {1,2}\{1,2\} and first term 11 which equals the sequence of run-lengths of itself, we call this K(1,2).K(1,2). We define K(m,n)K(m,n) similarly. A well-known conjecture is that the limiting density of K(1,2)K(1,2) is one-half. We state a natural generalization, the "generalized uniformness conjecture" (GUC). The GUC seems intractable, but we prove a partial result. The GUC implies that members of a certain family of directed graphs Gm,n,kG_{m,n,k} are all strongly connected. We prove this unconditionally. For d>0,d>0, let cf(m,n,d)cf(m,n,d) be the density of indices ii such that K(m,n)i=K(m,n)i+d.K(m, n)_i=K(m, n)_{i+d}. Essentially, cf(m,n,d)cf(m, n, d) is the autocorrelation function of a stationary stochastic process with random variables {Xt}tZ\{X_t\}_{t\in\mathbb{Z}} whereby a sample of a finite window of this process is formed by copying as many consecutive terms of K(m,n)K(m,n) starting from a "uniformly random index" iZ+.i\in\mathbb{Z}_+. Assuming the GUC, we prove that we can compute cf(m,n,d)cf(m,n,d) exactly for quite large dd by constructing a periodic sequence SS of period around 108.510^{8.5} such that for dd not too large, the correlation frequency at distance dd in K(m,n)K(m,n) equals that in S.S. We efficiently compute correlations in SS using polynomial multiplication via FFT. We plot our estimates cf(m,n,d)cf(m,n,d) for several small values of (m,n)(m,n) and d105d\le10^5 or 10610^6. We note many suggested patterns. For example, for the three pairs (m,n){(1,2),(2,3),(3,4)},(m,n)\in\{(1,2),(2,3),(3,4)\}, the function cf(m,n,d)cf(m,n,d) behaves very differently as we restrict dd to the m+nm+n residue classes mod\text{mod} m+n.m+n. The plots of the three functions cf(1,2,d),cf(2,3,d),cf(1,2,d),cf(2,3,d), and cf(3,4,d)cf(3,4,d) resemble waves which have common nodes. We consider this very unusual behavior for an autocorrelation function. The pairs (m,n){(1,4),(1,6),(2,5)}(m,n)\in\{(1,4),(1,6),(2,5)\} show wave-like patterns with much more noise.

Keywords

Cite

@article{arxiv.1703.00180,
  title  = {A uniformness conjecture of the Kolakoski sequence, graph connectivity, and correlations},
  author = {Bobby Shen},
  journal= {arXiv preprint arXiv:1703.00180},
  year   = {2017}
}

Comments

29 pages, 1 table, 16 figures, draft. arXiv admin note: text overlap with arXiv:1702.08156