Integrable boundary-value problems and nonlinear Fourier harmonics

For the nonlinear Schrödinger equation, the integrable boundary-value problem on a segment is considered. The concept of nonlinear ?-harmonics similar to the ordinary Fourier harmonics in the linear case is suggested. A solution of the initial boundary-value problem on the semiaxis is constructed by means of reduction to the Cauchy problem on the whole axis. Bibliography: 11 titles.