$\ell_2$-norm Flow Diffusion in Near-Linear Time

TL;DR

This paper introduces a nearly linear time randomized algorithm for $\, ext{ extlangle}2 ext{ extrangle}$-norm flow diffusion, enabling efficient graph clustering and cut detection beyond traditional random walk methods.

Contribution

It presents the first nearly linear time algorithm for $\, ext{ extlangle}2 ext{ extrangle}$-norm flow diffusion, with novel techniques for handling constraints in graph optimization.

Findings

Algorithm runs in $\, ilde{O}(m)$ time for large graphs.

Enables efficient detection of low conductance cuts.

Provides an alternative approach to graph clustering problems.

Abstract

Diffusion is a fundamental graph procedure and has been a basic building block in a wide range of theoretical and empirical applications such as graph partitioning and semi-supervised learning on graphs. In this paper, we study computationally efficient diffusion primitives beyond random walk. We design an $\widetilde{O}(m)$-time randomized algorithm for the $\ell_2$-norm flow diffusion problem, a recently proposed diffusion model based on network flow with demonstrated graph clustering related applications both in theory and in practice. Examples include finding locally-biased low conductance cuts. Using a known connection between the optimal dual solution of the flow diffusion problem and the local cut structure, our algorithm gives an alternative approach for finding such cuts in nearly linear time. From a technical point of view, our algorithm contributes a novel way of dealing with inequality constraints in graph optimization problems. It adapts the high-level algorithmic framework of nearly linear time Laplacian system solvers, but requires several new tools: vertex elimination under constraints, a new family of graph ultra-sparsifiers, and accelerated proximal gradient methods with inexact proximal mapping computation.