Computable Characterisations of Scaled Relative Graphs of Closed Operators

Abstract: Scaled Relative Graphs (SRGs) provide a promising tool for stability and robustness analysis of multi-input-multi-output systems. In this paper, we provide tools for exact and computable constructions of the SRG for closed linear operators, based on maximum and minimum gain computations. The results are suitable for bounded and unbounded operators, and we specify how they can be used to draw SRGs for the typical operators that are used to model linear-time-invariant dynamical systems. Furthermore, for the special case of state-space models, we show how the Bounded Real Lemma can be used to construct the SRG.