Evaluation of suboptimality and sensitivity in control and filtering processes

In the context of modern control theory, optimum performance of a system is of primary concern. In most applications, however, one must be satisfied with something short of optimum performance as a consequence of the use of a suboptimal controller or plant parameter variations. Using a scalar measure for the deviation of the actual performance, a general approach to the evaluation of suboptimality and sensitivity for control and filtering processes is suggested. Some specific results involving only algebraic conditions are obtained.