## Boundary Integral Equations: tutorials and resources

#### Alex Barnett

Boundary integral equations (BIEs) are a wonderfully efficient way to solve PDE boundary value problems (BVPs) or eigenvalue problems (EVPs) with constant (or piecewise-constant) coefficients. This includes elliptic PDE such as the Laplace, Helmholtz, Maxwell, and Stokes equations. Much of my recent research is on better ways to do this. Here are some resources on theory and numerical methods.

### Mathematical theory resources

• David Colton and Rainer Kress, Integral equation methods in scattering theory (Wiley, 1983). Helmholtz and Maxwell equations in 3D. Chapter 3 has useful proofs including the "inside-out" trick for existence for the transmission BVP.
• David Colton and Rainer Kress, Inverse acoustic and electromagnetic scattering theory (Springer, 1998). Has a good summary for the Helmholtz (including the 2D case, and numerics including the Martensen-Kussmaul spectral quadrature) and Maxwell equations.
• David Colton, Partial Differential Equations: An Introduction (Random House, 1988). Unusally detailed on Bessel functions and the Helmholtz equation in 2D. Includes proof of jump relations that relies on "blurring" the boundary.
• Rainer Kress, Linear Integral Equations (Springer, 1999). Chapter 6 has potential theory for Laplace equation. Chapter 12 has the Nystrom method.
• My handwritten class notes for Math 126. Starting at p.25, although the earlier stuff is useful numerical analysis background. This draws from the above Kress and Colton books.

### Numerical methods and resources for coding schemes yourself

Established numerical methods:

• My tutorials from our 2014 CBMS conference:
• Review and comparison article by myself with Gunnar Martinsson, Sijia Hao, and Patrick Young (2011). Covers mostly the Helmholtz 2D case on smooth curves, which involves logarithmically singular kernels.

More advanced numerical methods and research for BVPs:

Methods specific to eigenvalue problems:

### Existing software packages

• MPSpack includes code for Laplace and Helmholtz BIEs in 2D, including various quadrature schemes for smooth curves and corners, and periodization methods. The tutorial (Sec. 7-9) has the BIE commands.
• My BIE2D Matlab software package (to follow...)
• FMM
• etc

This work is enabled in part by NSF grant DMS-1216656.