Software used for the simulations presented in 'Robustness of subwavelength devices: a case study of cochlea-inspired rainbow sensors' by B. Davies and L. Herren (2021). The code uses the multipole expansion method (in combination with an asymptotic approximation by the generalised capacitance matrix) to simulate the resonant properties of an array of subwavelength resonators which has been designed to act as a cochlea-inspired rainbow sensor. Various perturbations of the structure are simulated, to demonstrate its stability and robustness.