In a recent paper, Giust et al. showed how the elements of the 2x2 scattering matrix of a one-dimensional system composed of two subsystems can be expressed in terms of the scattering amplitudes of the individual subsystems to generalize Einstein’s composition law of velocities. We note that this factorization property [...].

Sassoli de Bianchi, M. (2011). Comment on “Generalized composition law from 2x2 matrices,” by R. Giust, J.-M. Vigoureux, and J. Lages [Am. J. Phys. 77 (11), 1068–1073 (2009)]. Am. J. Phys. 79, pp. 546-549. Doi: 10.1119/1.3549205.