ABSTRACT
In the previous section we have shown how the details of a proposed Nyquist locus are related to various aspects of the closed-loop system performance. What prevents the policy designer from achieving any locus he wants, and thus obtaining any performance characteristics that he specified? Factors of two kinds impede him. There are factors that are inherent to the mathematics and to the particular economy with which he is working - we assume that he can do nothing to make the economy itself easier to control - and there are factors that arise from practical considerations - how vigorously he can move the policy instruments, for instance, and how complex the policy can be. In this section we shall focus on the inherent limitations to policy performance.
