On nonreflecting boundary conditions (Q1908725)

This paper contributes to the study of nonreflecting boundary conditions at artificial boundaries for use with the Helmholtz equation. The following developments are covered: -- How to remove the difficulties that arise when the exact Dirichlet-to-Neumann condition is truncated? -- The exact boundary condition for elliptical and spheroidal coordinates and the approximate local boundary conditions. -- A sequence of new and more accurate local boundary conditions is derived for polar coordinates in two dimensions. -- Some numerical results are presented.