ABSTRACT
As has been shown in Chapter 1, adjoint operators in non-linear problems may be defined in different ways. This raises a reasonable question of correlation between different adjoint operators corresponding to the same non-linear problem. At the same time, the problem of choosing the ‘best’ (in a sense) adjoint operator is of interest (from the numerical point of view). The solution of this problem will help to justify perturbation algorithms being applied in non-linear problems. There are a number of other questions and problems to be answered in the adjoint equation theory for a prescribed class of problems. Some of these questions are studied in this chapter.
