Boundary conditions for polarized radiative transfer with incident radiation

Context. Polarized radiative transfer in the presence of scattering in spectral lines and/or in continua may be cast in a reduced form for six reduced components of the radiation field. In this formalism, the six components of the reduced source function are angle-independent quantities. It thus drastically reduces the storage requirement of numerical codes and it is very well suited to solving polarized non-local thermodynamic equilibrium radiative transfer problems in 3D media.