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We present a scheme to solve the nonlinear multigroup radiation diffusion(MGD) equations. The method is incorporated into a massively parallel,multidimensional, Eulerian radiation-hydrodynamic code with adaptive meshrefinement (AMR). The patch-based AMR algorithm refines in both space and timecreating a hierarchy of levels, coarsest to finest. The physics modules aretime-advanced using operator splitting. On each level, separate level-solvepackages advance the modules. Our multigroup level-solve adapts an implicitprocedure which leads to a two-step iterative scheme that alternates betweenelliptic solves for each group with intra-cell group coupling. For robustness,we introduce pseudo transient continuation (PTC). We analyze the magnitude ofthe PTC parameter to ensure positivity of the resulting linear system, diagonaldominance and convergence of the two-step scheme. For AMR, a level defines asubdomain for refinement. For diffusive processes such as MGD, the refinedlevel uses Dirichet boundary data at the coarse-fine interface and the data isderived from the coarse level solution. After advancing on the fine level, anadditional procedure, the sync-solve (SS), is required in order to enforceconservation. The MGD SS reduces to an elliptic solve on a combined grid for asystem of G equations, where G is the number of groups. We adapt the partialtemperature scheme for the SS; hence, we reuse the infrastructure developed forscalar equations. Results are presented. (Abridged)

A multigroup diffusion solver using pseudo transient continuation for a radiation-hydrodynamic code with patch-based AMR