On the solution of the integral equation of scattering for finite range potentials

In the problem of the scattering of a particle in the presence of a finite range central potential, the integral equation for the lth partial wave is studied. By using a matrix method, the exact external solutions are expressed in terms of the Fredholm determinant ?, and the phase of ? turns out to be equal to the phase shift. As an example, an array of delta-shell potentials is considered.