Trefftz absorbing boundary conditions in analytical, Discontinuous Galerkin and Finite difference form

We explore a novel avenue for generating absorbing boundary conditions for wave problems. The key part of our approach is Trefftz approximations of the solution, i.e. approximations by functions satisfying locally the underlying wave equation. Trefftz functions include outgoing waves only (and possibly evanescent waves), but no incoming waves. We show how this idea can be applied in three different contexts: analytical, Discontinuous Galerkin, and finite difference.