On iterative solutions of the LTE model atmospheric problem

Iterative methods for solving the coupled radiative-transfer and energy-balance equations in the LTE model atmospheres problem including isotropic coherent scattering are discussed. It is shown that iterative solution (e.g. by SOR techniques) of the grand matrix encountered in such problems is vastly more efficient than a direct solution, and is easily vectorized. The final computational effort is linear in the number of depths and frequencies considered, and thus this approach opens the door for the computation of both static and dynamic line-blanketed models using large numbers of depth-points and huge numbers of frequencies. The iterative methods discussed here can be applied to line formation problems with complete redistribution and to certain classes of problems with partial redistribution (e.g. Compton scattering problems in the Fokker-Planck approximation). (author)