English

Dynamically Defined Sequences with Small Discrepancy

Combinatorics 2019-07-16 v2 Classical Analysis and ODEs Number Theory

Abstract

We study the problem of constructing sequences (xn)n=1(x_n)_{n=1}^{\infty} on [0,1][0,1] in such a way that DN=sup0x1{1iN:xix}Nx D_N^* = \sup_{0 \leq x \leq 1} \left| \frac{ \left\{1 \leq i \leq N: x_i \leq x \right\}}{N} - x \right| is uniformly small. A result of Schmidt shows that necessarily DN(logN)N1D_N^* \gtrsim (\log{N}) N^{-1} for infinitely many NN and there are several classical constructions attaining this growth. We describe a type of uniformly distributed sequence that seems to be completely novel: given {x1,,xN1}\left\{x_1, \dots, x_{N-1} \right\}, we construct xNx_N in a greedy manner xN=argminminkxxkN10k=1N11log(2sin(πxxk)). x_N = \arg\min_{\min_k |x-x_k| \geq N^{-10}} \sum_{k=1}^{N-1}{1-\log{(2\sin{(\pi |x-x_k|)})}}. We prove that DN(logN)N1/2D_N \lesssim (\log{N}) N^{-1/2} and conjecture that DN(logN)N1D_N \lesssim (\log{N}) N^{-1}. Numerical examples illustrate this conjecture in a very impressive manner. We also establish a discrepancy bound DN(logN)dN1/2D_N \lesssim (\log{N})^d N^{-1/2} for an analogous construction in higher dimensions and conjecture it to be DN(logN)dN1D_N \lesssim (\log{N})^d N^{-1}.

Keywords

Cite

@article{arxiv.1902.03269,
  title  = {Dynamically Defined Sequences with Small Discrepancy},
  author = {Stefan Steinerberger},
  journal= {arXiv preprint arXiv:1902.03269},
  year   = {2019}
}