Fast Expansion into Harmonics on the Disk

The dataset used in this paper is a set of L x L images representing functions on [-1, 1]^2 supported on the disk {x ∈ R^2 : |x| < 1}. The images are digitized and the authors present a fast and numerically accurate method for expanding these images into the harmonics (Dirichlet Laplacian eigenfunctions) on the disk.