Two-dimensional Fourier Continuation and applications

TL;DR

This paper introduces a two-dimensional Fourier Continuation method (2D-FC) for extending smooth functions on complex domains, enabling high-order accurate solutions to PDEs with efficient algorithms and applications to wave and Poisson equations.

Contribution

The paper develops a novel 2D-FC technique that generalizes Fourier continuation to two dimensions and applies it to solve PDEs efficiently on general domains.

Findings

Achieves arbitrarily high order accuracy.

Enables efficient solutions to wave and Poisson equations.

Introduces the Fourier Forwarding solver with sublinear cost.

Abstract

This paper presents a "two-dimensional Fourier Continuation" method (2D-FC) for construction of bi-periodic extensions of smooth non-periodic functions defined over general two-dimensional smooth domains. The approach can be directly generalized to domains of any given dimensionality, and even to non-smooth domains, but such generalizations are not considered here. The 2D-FC extensions are produced in a two-step procedure. In the first step the one-dimensional Fourier Continuation method is applied along a discrete set of outward boundary-normal directions to produce, along such directions, continuations that vanish outside a narrow interval beyond the boundary. Thus, the first step of the algorithm produces "blending-to-zero along normals" for the given function values. In the second step, the extended function values are evaluated on an underlying Cartesian grid by means of an efficient, high-order boundary-normal interpolation scheme. A Fourier Continuation expansion of the given function can then be obtained by a direct application of the two-dimensional FFT algorithm. Algorithms of arbitrarily high order of accuracy can be obtained by this method. The usefulness and performance of the proposed two-dimensional Fourier Continuation method are illustrated with applications to the Poisson equation and the time-domain wave equation within a bounded domain. As part of these examples the novel "Fourier Forwarding" solver is introduced which, propagating plane waves as they would in free space and relying on certain boundary corrections, can solve the time-domain wave equation and other hyperbolic partial differential equations within general domains at computing costs that grow sublinearly with the size of the spatial discretization.