A boundary integral algorithm for the Laplace Dirichlet-Neumann mixed eigenvalue problem

TL;DR

This paper introduces a high-accuracy boundary integral algorithm for solving Laplace eigenvalue problems with mixed Dirichlet-Neumann boundary conditions, applicable to smooth and non-smooth domains, enabling efficient computation of many eigenvalues.

Contribution

The paper develops a novel integral-equation method that accurately computes Zaremba eigenvalues and eigenfunctions for complex geometries, incorporating singularity handling and stabilization techniques.

Findings

High-order convergence achieved without fine meshes

Effective handling of boundary singularities with Fourier Continuation

Rapid computation of numerous eigenvalues with near double-precision accuracy

Abstract

We present a novel integral-equation algorithm for evaluation of Zaremba eigenvalues and eigenfunctions}, that is, eigenvalues and eigenfunctions of the Laplace operator with mixed Dirichlet-Neumann boundary conditions; of course, (slight modifications of) our algorithms are also applicable to the pure Dirichlet and Neumann eigenproblems. Expressing the eigenfunctions by means of an ansatz based on the single layer boundary operator, the Zaremba eigenproblem is transformed into a nonlinear equation for the eigenvalue $\mu$. For smooth domains the singular structure at Dirichlet-Neumann junctions is incorporated as part of our corresponding numerical algorithm---which otherwise relies on use of the cosine change of variables, trigonometric polynomials and, to avoid the Gibbs phenomenon that would arise from the solution singularities, the Fourier Continuation method (FC). The resulting numerical algorithm converges with high order accuracy without recourse to use of meshes finer than those resulting from the cosine transformation. For non-smooth (Lipschitz) domains, in turn, an alternative algorithm is presented which achieves high-order accuracy on the basis of graded meshes. In either case, smooth or Lipschitz boundary, eigenvalues are evaluated by searching for zero minimal singular values of a suitably stabilized discrete version of the single layer operator mentioned above. (The stabilization technique is used to enable robust non-local zero searches.) The resulting methods, which are fast and highly accurate for high- and low-frequencies alike, can solve extremely challenging two-dimensional Dirichlet, Neumann and Zaremba eigenproblems with high accuracies in short computing times---enabling, in particular, evaluation of thousands of eigenvalues and corresponding eigenfunctions for a given smooth or non-smooth geometry with nearly full double-precision accuracy