## ABSTRACT

In deciding on a principle of construction of adjoint equations, one is to take proper account of the objectives to be pursued in the problems under consideration (finding the corrections to solutions, computing the functionals, choosing the control parameters, etc.). In addition, one should ensure the solvability of adjoint equations If the problem on development of perturbation algorithms is attacked, the adjoint equations are wanted to be correctly solvable as it is a relatively simple matter in this case to justify perturbation algorithms both of small and of the N-th order. It may be also suggested that, in general, one may be hard pressed to find the ‘optimal’ principle of construction of adjoint equations, and it would be appropriate to solve this problem for each specific case. This chapter considers similar cases that have arisen in transport theory problems. We discuss, as a rule, the possibility of application of perturbation algorithms for solving the problem under consideration, based on the solution of main and adjoint equations.