Asymptotics of Greedy Energy Points

TL;DR

This paper studies the asymptotic behavior of greedy energy points, known as Leja points, on compact sets, providing conditions for their energy optimality and analyzing specific cases like Riesz kernels.

Contribution

It establishes sufficient conditions for greedy energy points to be asymptotically energy minimizing and describes their distribution, with new insights for Riesz kernels on various geometries.

Findings

Greedy points are asymptotically energy minimizing under certain conditions.

For Riesz kernels with s>1 on curves, greedy points are not energy minimizing.

On spheres and for weighted kernels, additional asymptotic behaviors are characterized.

Abstract

For a symmetric kernel $k:X\times X \to \mathbb{R}\cup\{+\infty\}$ on a locally compact Hausdorff space $X$, we investigate the asymptotic behavior of greedy $k$-energy points $\{a_{i}\}_{1}^{\infty}$ for a compact subset $A\subset X$ that are defined inductively by selecting $a_{1}\in A$ arbitrarily and $a_{n+1}$ so that $\sum_{i=1}^{n}k(a_{n+1},a_{i})=\inf_{x\in A}\sum_{i=1}^{n}k(x,a_{i})$. We give sufficient conditions under which these points (also known as Leja points) are asymptotically energy minimizing (i.e. have energy $\sum_{i\neq j}^{N}k(a_{i},a_{j})$ as $N\to\infty$ that is asymptotically the same as $\mathcal{E}(A,N):=\min\{\sum_{i\neq j}k(x_{i},x_{j}):x_{1},...,x_{N}\in A\}$), and have asymptotic distribution equal to the equilibrium measure for $A$. For the case of Riesz kernels $k_{s}(x,y):=|x-y|^{-s}$, $s>0$, we show that if $A$ is a rectifiable Jordan arc or closed curve in $\mathbb{R}^{p}$ and $s>1$, then greedy $k_{s}$-energy points are not asymptotically energy minimizing, in contrast to the case $s<1$. (In fact we show that no sequence of points can be asymptotically energy minimizing for $s>1$.) Additional results are obtained for greedy $k_{s}$-energy points on a sphere, for greedy best-packing points, and for weighted Riesz kernels.