Ray Casting and Flux Limited Diffusion

Solving radiative transfer problems with ray casting methods is compared with the commonly used `Flux Limited Diffusion' approximation. Whereas ray casting produces solutions that converge to the exact one as the number of rays is increased, flux-limited-diffusion is fundamentally a `look-alike' method, which produces solutions that are reminiscent of the correct solution but which cannot be made to converge to it.