A VARIATIONAL CHARACTERIZATION OF EQUATION OF TRANSFER

A variational principle is presented which allows one to obtain a variational estimate of an arbitrary functional of the solution to the equation of radiative transfer. It is shown that this functional can be derived, in contrast to the usual variational procedure of guessing a functional and then proving correctness. It is further shown that if this functional is viewed in the Lagrangian sense, all reference to the adjoint equation can be eliminated. Hence to derive approximate descriptions of radiative transfer one only requires a trial function for the specific intensity. A generalization of the Eddington approximation based on this formalism is suggested. © 1969.