Hybrid Adaptive Ray-Moment Method (HARM$^2$): A Highly Parallel Method   for Radiation Hydrodynamics on Adaptive Grids
  We present a highly-parallel multi-frequency hybrid radiation hydrodynamics algorithm that combines a spatially-adaptive long characteristics method for the radiation field from point sources with a moment method that handles the diffuse radiation field produced by a volume-filling fluid. Our Hybrid Adaptive Ray-Moment Method (HARM$^2$) operates on patch-based adaptive grids, is compatible with asynchronous time stepping, and works with any moment method. In comparison to previous long characteristics methods, we have greatly improved the parallel performance of the adaptive long-characteristics method by developing a new completely asynchronous and non-blocking communication algorithm. As a result of this improvement, our implementation achieves near-perfect scaling up to $\mathcal{O}(10^3)$ processors on distributed memory machines. We present a series of tests to demonstrate the accuracy and performance of the method. 
Anna L. Rosen, Mark R. Krumholz, Jeffrey S. Oishi, Aaron T. Lee, and   Richard I. Klein
astro-ph.IM astro-ph.SR physics.comp-ph