An optimal cascadic multigrid method for the radiative transfer equation

This paper presents a fast and optimal multigrid solver for the radiative transfer equation. A discrete-ordinate discontinuous-streamline diffusion method is employed to discretize the radiative transfer equation. Instead of utilizing conventional multigrid methods for spatial variables only, a spatial cascadic multigrid method and a full cascadic multigrid method are developed to achieve rapid convergence in iterative calculation. Preliminary analysis is also conducted, suggesting the optimal convergence rate. Numerical tests show a significant reduction of the computational time compared to conventional iterative methods for the radiative transfer equation.