The Heun equation and the Calogero-Moser-Sutherland system V: generalized Darboux transformations

Abstract

We obtain isomonodromic transformations for Heun’s equation by generalizing the Darboux transformation, and we find pairs and triplets of Heun’s equation which have the same monodromy structure. By composing generalized Darboux transformations, we establish a new construction of the commuting operator which ensures that the finite-gap property is satisfied. As an application, we prove some previous conjectures in part III.