Noel J. Walkington

2papers

2 Papers

LGApr 20, 2020
Weighted Cheeger and Buser Inequalities, with Applications to Clustering and Cutting Probability Densities

Timothy Chu, Gary L. Miller, Noel J. Walkington et al.

In this paper, we show how sparse or isoperimetric cuts of a probability density function relate to Cheeger cuts of its principal eigenfunction, for appropriate definitions of `sparse cut' and `principal eigenfunction'. We construct these appropriate definitions of sparse cut and principal eigenfunction in the probability density setting. Then, we prove Cheeger and Buser type inequalities similar to those for the normalized graph Laplacian of Alon-Milman. We demonstrate that no such inequalities hold for most prior definitions of sparse cut and principal eigenfunction. We apply this result to generate novel algorithms for cutting probability densities and clustering data, including a principled variant of spectral clustering.

NAMar 30, 2016
Dual-Mixed Finite Element Methods for the Navier-Stokes Equations

Jason S. Howell, Noel J. Walkington

A mixed finite element method for the Navier-Stokes equations is introduced in which the stress is a primary variable. The variational formulation retains the mathematical structure of the Navier-Stokes equations and the classical theory extends naturally to this setting. Finite element spaces satisfying the associated inf-sup conditions are developed.