A posteriori finite element error bounds for non-linear outputs of the Helmholtz equation

A Neumann subproblem a posteriori finite element procedure for the efficient and accurate calculation of rigorous, constant-free upper and lower bounds for non-linear outputs of the Helmholtz equation in two-dimensional exterior domains is presented. The bound procedure is firstly formulated, with particular emphasis on appropriate extension to complex-valued equations; then, illustrative numerical examples for outputs, such as the intensity of the scattered wave over a small segment of the domain boundary, are provided.Peer Reviewe