Linear time computation of robust stability margins

Applying recent results for feasible regions of compensation, we introduce an optimal algorithm for computing combined phase and gain stability margins. We consider the case of a rational transfer function with independent interval uncertainty in the numerator and denominator. For any given frequency, our algorithm expresses the minimal complex perturbation that destabilizes the transfer function. We furnish an example that contrasts our results with classical margins for gain and phase, as well as with the structured singular value μ