  The transition-matrix ($T$-matrix) approach provides a general formalism to
study scattering problems in various areas of physics, including acoustics
(scalar fields) and electromagnetics (vector fields), and is related to the
theory of the scattering matrix ($S$-matrix) used in quantum mechanics and
quantum field theory. Focusing on electromagnetic scattering, we highlight an
alternative formulation of the $T$-matrix approach, based on the use of the
reactance matrix or $K$-matrix, which is more suited to formal studies of
energy conservation constraints (such as the optical theorem). We show in
particular that electrostatics or quasi-static approximations can be corrected
within this framework to satisfy the energy conservation constraints associated
with radiation. A general formula for such a radiative correction is explicitly
obtained, and empirical expressions proposed in earlier studies are shown to be
special cases of this general formula. This work therefore provides a
justification of the empirical radiative correction to the dipolar
polarizability and a generalization of this correction to any types of point or
body scatterers of arbitrary shapes, including higher multipolar orders.
