English

Oscillatory functions vanish on a large set

Classical Analysis and ODEs 2018-05-09 v2 Analysis of PDEs

Abstract

Let (M,g)(M,g) be a nn-dimensional, compact Riemannian manifold. We define the frequency scale λ\lambda of a function fC0(M)f \in C^{0}(M) as the largest number such that f,ϕk=0\left\langle f, \phi_k \right\rangle =0 for all Laplacian eigenfunctions with eigenvalue λkλ\lambda_k \leq \lambda. If λ\lambda is large, then the function ff has to vanish on a large set Hn1{x:f(x)=0}(fL1fL)21nλ(logλ)n/2. \mathcal{H}^{n-1} \left\{x:f(x) =0\right\} \gtrsim_{} \left( \frac{ \|f\|_{L^1}}{\|f\|_{L^{\infty}}} \right)^{2 - \frac{1}{n}} \frac{ \sqrt{\lambda}}{(\log{\lambda})^{n/2}}. Trigonometric functions on the flat torus Td\mathbb{T}^d show that the result is sharp up to a logarithm if fL1fL\|f\|_{L^1} \sim \|f\|_{L^{\infty}}. We also obtain a stronger result conditioned on the geometric regularity of {x:f(x)=0}\left\{x:f(x) = 0\right\}. This may be understood as a very general higher-dimensional extension of the Sturm oscillation theorem.

Keywords

Cite

@article{arxiv.1708.05373,
  title  = {Oscillatory functions vanish on a large set},
  author = {Stefan Steinerberger},
  journal= {arXiv preprint arXiv:1708.05373},
  year   = {2018}
}

Comments

v2, slightly improved results

R2 v1 2026-06-22T21:17:24.414Z