One of the main tasks when designing QFT robust controllers is the definition of the plant frequency response, taking into account the complete n-dimensional space of model plant uncertainty. Consider an uncertain plant P, where P ∈ P, and P is the set of possible plants due to uncertainty, such that,
TP(jωi) is the associated template for ω = ω i , that is to say, the set of complex numbers representing the frequency response of the uncertain plant at a fixed frequency ω i . In other words, it is the projection of the n-dimensional parameter space onto ℜ2, according to the plant transfer function P for a given frequency (see Fig. A.1).