Least-squares method in scattering theory

A particular least-squares method is presented for the calculation of inelastic scattering wave functions by an expansion technique. The variational procedure is based on a convenient error functional. The test-function space is spanned by a finite set of square-integrable (Hilbert-space) basis functions. The open-channel orbitals include the Kohn-Hulth\'en--type oscillatory terms of nonvanishing asymptotic amplitudes. The error functional involves only bound-bound and bound-free matrix elements. Criteria are given to select acceptable approximations. Two-channel calculations show that the zero-order results of this method have an accuracy comparable to the first-order results of earlier calculations. No anomalies are encountered.