  Practical methods to compute dipole strengths for a three-body system by
using a discretized continuum are analyzed. New techniques involving Green's
function are developed, either by correcting the tail of the approximate wave
function in a direct calculation of the strength function or by using a
solution of a driven Schroedinger equation in a summed expression of the
strength. They are compared with the complex scaling method and the Lorentz
integral transform, also making use of a discretized continuum. Numerical tests
are performed with a hyperscalar three-body potential in the
hyperspherical-harmonics formalism. They show that the Lorentz integral
transform method is less practical than the other methods because of a
difficult inverse transform. These other methods provide in general comparable
accuracies.
