Radiative perturbation theory: a review

Radiative perturbation theory is a computational technique which can greatly ease the burden of repeated solution of the radiative transfer equation for model atmospheres which differ from one another by only relatively small changes in some of the optical parameters. It requires the solution of both the radiative transfer equation, and its adjoint, followed by some usually straightforward integrations of these solutions. In this work we review the theoretical structure of the technique, and discuss a series of applications which have already demonstrated its utility. Future developments of the theory, and new applications currently under consideration, are also discussed.