Paper detail

On the behavior of $1$-Laplacian Ratio Cuts on nearly rectangular domains

Given a connected set $Ω_0 \subset \mathbb{R}^2$, define a sequence of sets $(Ω_n)_{n=0}^{\infty}$ where $Ω_{n+1}$ is the subset of $Ω_n$ where the first eigenfunction of the (properly normalized) Neumann $p-$Laplacian $ -Δ^{(p)} ϕ= λ_1 |ϕ|^{p-2} ϕ$ is positive (or negative). For $p=1$, this is also referred to as the Ratio Cut of the domain. We conjecture that, unless $Ω_0$ is an isosceles right triangle, these sets converge to the set of rectangles with eccentricity bounded by 2 in the Gromov-Hausdorff distance as long as they have a certain distance to the boundary $\partial Ω_0$. We establish some aspects of this conjecture for $p=1$ where we prove that (1) the 1-Laplacian spectral cut of domains sufficiently close to rectangles of a given aspect ratio is a circular arc that is closer to flat than the original domain (leading eventually to quadrilaterals) and (2) quadrilaterals close to a rectangle of aspect ratio $2$ stay close to quadrilaterals and move closer to rectangles in a suitable metric. We also discuss some numerical aspects and pose many open questions.