English

Positive-definite Functions, Exponential Sums and the Greedy Algorithm: a curious Phenomenon

Classical Analysis and ODEs 2020-04-08 v3 Number Theory

Abstract

We describe a curious dynamical system that results in sequences of real numbers in [0,1][0,1] with seemingly remarkable properties. Let the function f:TRf:\mathbb{T} \rightarrow \mathbb{R} satisfy f^(k)ck2\hat{f}(k) \geq c|k|^{-2} and define a sequence via xn=argminxk=1n1f(xxk). x_n = \arg\min_x \sum_{k=1}^{n-1}{f(x-x_k)}. Such sequences (xn)n=1(x_n)_{n=1}^{\infty} seem to be astonishingly regularly distributed in various ways (satisfying favorable exponential sum estimates; every interval J[0,1]J \subset [0,1] contains Jn\sim |J|n elements). We prove W2(1nk=1nδxk,dx)cn, W_2\left( \frac{1}{n} \sum_{k=1}^{n}{\delta_{x_k}}, dx\right) \leq \frac{c}{\sqrt{n}}, where W2W_2 is the 2-Wasserstein distance. Much stronger results seem to be true and it seems like an interesting problem to understand this dynamical system better. We obtain optimal results in dimension d3d \geq 3: using G(x,y)G(x,y) to denote the Green's function of the Laplacian on a compact manifold, we show that xn=argminxMk=1n1G(x,xk)\mboxsatisfiesW2(1nk=1nδxk,dx)1n1/d. x_n = \arg\min_{x \in M} \sum_{k=1}^{n-1}{G(x,x_k)} \quad \mbox{satisfies} \quad W_2\left( \frac{1}{n} \sum_{k=1}^{n}{\delta_{x_k}}, dx\right) \lesssim \frac{1}{n^{1/d}}.

Keywords

Cite

@article{arxiv.1908.11228,
  title  = {Positive-definite Functions, Exponential Sums and the Greedy Algorithm: a curious Phenomenon},
  author = {Louis Brown and Stefan Steinerberger},
  journal= {arXiv preprint arXiv:1908.11228},
  year   = {2020}
}
R2 v1 2026-06-23T10:59:57.298Z