On the regularization of Cauchy-type integral operators via the density interpolation method and applications

TL;DR

This paper introduces a regularization method for high-order numerical evaluation of nearly singular Cauchy-type integrals using density interpolation, enabling accurate computations near and on contours with applications to Laplace potentials and conformal mappings.

Contribution

It proposes a novel regularization technique based on density interpolation and complex analysis tools, improving accuracy and efficiency over existing methods for evaluating singular integrals.

Findings

Significant accuracy improvements in evaluating Laplace layer potentials.

Effective regularization of nearly singular and hypersingular integrals.

Successful application to conformal mapping computations.

Abstract

This paper presents a regularization technique for the high order efficient numerical evaluation of nearly singular, principal-value, and finite-part Cauchy-type integral operators. By relying on the Cauchy formula, the Cauchy-Goursat theorem, and on-curve Taylor interpolations of the input density, the proposed methodology allows to recast the Cauchy and associated integral operators as smooth contour integrals. As such, they can be accurately evaluated everywhere in the complex plane -- including at problematic points near and on the contour -- by means of elementary quadrature rules. Applications of the technique to the evaluation of the Laplace layer potentials and related integral operators, as well as to the computation conformal mappings, are examined in detail. The former application, in particular, amounts to a significant improvement over the recently introduced harmonic density interpolation method. Spectrally accurate discretization approaches for smooth and piecewise smooth contours are presented. A variety of numerical examples, including the solution of weakly singular and hypersingular Laplace boundary integral equations, and the evaluation of challenging conformal mappings, demonstrate the effectiveness and accuracy of the density interpolation method in this context.