Fast algorithms for Quadrature by Expansion I: Globally valid expansions
This work provides a black-box method for efficiently and accurately evaluating layer potentials in integral equation solvers for PDE boundary value problems.
The authors developed a unified numerical scheme coupling Quadrature by Expansion with a customized Fast Multipole Method for the Helmholtz equation in 2D, enabling linear-time evaluation of layer potentials with user-chosen accuracy. Numerical examples demonstrate speed and accuracy.
The use of integral equation methods for the efficient numerical solution of PDE boundary value problems requires two main tools: quadrature rules for the evaluation of layer potential integral operators with singular kernels, and fast algorithms for solving the resulting dense linear systems. Classically, these tools were developed separately. In this work, we present a unified numerical scheme based on coupling Quadrature by Expansion, a recent quadrature method, to a customized Fast Multipole Method (FMM) for the Helmholtz equation in two dimensions. The method allows the evaluation of layer potentials in linear-time complexity, anywhere in space, with a uniform, user-chosen level of accuracy as a black-box computational method. Providing this capability requires geometric and algorithmic considerations beyond the needs of standard FMMs as well as careful consideration of the accuracy of multipole translations. We illustrate the speed and accuracy of our method with various numerical examples. Keywords: Layer Potentials; Singular Integrals; Quadrature; High-order accuracy; Integral equations; Helmholtz equation; Fast multipole method.