“…Then, the eigenvalues of Equations coincide with the eigenvalues of Equations , where f 1 ( λ ):= ψ ( π , λ ), f 2 ( λ )=− ψ ′ ( π , λ ). Note that these functions f j ( λ ), j =1,2, can be determined by the given potential q ( x ), x ∈( π ,2 π ).In recent years, Inverse Problem was generalized to the case when the potential is known not on the half but on an arbitrary part ( a ,2 π ) of the interval (see Gesztesy and Simon and Horváth), to discontinuous Sturm–Liouville operators (see Hald, Shieh et al, and Yang and Bondarenko) and to differential operators on metric graphs (see other studies). Differential operators with discontinuities arise in geophysical models of the Earth oscillations (see Anderssen and Lapwood and Usami) and in electronics for constructing parameters of heterogeneous electronic lines with desirable technical characteristics (see Meschanov and Feldstein).…”