Robust stabilization: a piece of cake

Considers a non-parametric model for plant uncertainty where at each frequency the plant error is constrained to a sector (the proverbial piece of cake) of the complex plane. Most importantly, the sector corner Z₀(ω) and the sector angle φ(ω) are allowed to change with frequency. Thus, both frequency-dependent magnitude and phase information of the plant error are modelled. It is shown that the associated robust stabilization problem is equivalent to a standard Nevanlinna-Pick interpolation problem