Cooperative relaxation methods for multigroup radiation diffusion in radiation hydrodynamics

With restrictive Courant criteria, the time integration of a radiation diffusion equation is generally done by a fully or partially implicit method. Relaxation methods are often effective and cooperative relaxation refers to a technique that will diffuse each spectral radiation group as a separate operation and combine the changes to a full spectrum. Successive passes over the groups provide convergence, as well as conserving energy over time, space and spectrum. Linearized and fully nonlinear variations on the method are discussed.