Convergence to Radial Symmetry in Iterative Convolution-Thresholding Dynamics

Abstract

We study a discrete-time spatially extended dynamical system motivated by the continuum limit of binary neuron networks on geometric random graphs. The model evolves a function $\ddot{I}ˆ:{\mathbb{R}}^d\to [0,1]$ by iterative smoothing and sharpening; that is, $\ddot{I}{ˆ}_{t+1}={\hat{I}}_t^3\circ (g\ast \ddot{I}{ˆ}_t)$, where $g$ is a radial convolution kernel and ${\hat{I}}_t^3$ is a monotone map. Under mild regularity conditions on $g$ and ${\hat{I}}_t^3$, we prove that $\ddot{I}{ˆ}_t$ tends toward radial symmetry as $t\to \infty$. Notably, a special case of this process recovers the Merriman-Bence-Osher (MBO) scheme for the motion of interfaces by mean curvature, and we provide a novel analysis of its behavior. Our results connect the dynamics of spatial binary neuron networks with classical models of interface motion, and we establish general conditions under which spatial dependence drives activity toward radial symmetry.

27 pages, 5 figures