Subgradient algorithm for computing contraction metrics for equilibria

We propose a subgradient algorithm for the computation of contraction metrics for systems with an exponentially stable equilibrium. We show that for sufficiently smooth systems our method is always able to compute a contraction metric on any forward-invariant compact neighbourhood of the equilibrium, which is a subset its basin of attraction. We demonstrate the applicability of our method by constructing contraction metrics for three planar and one three-dimensional systems.