标题： TREVR: 一种通用的$N log^2 N$辐射传输算法 显示英文标题

标题： TREVR: A general $N log^2 N$ radiative transfer algorithm

摘要： 我们提出了TREVR（基于树的逆向光线追踪），这是一种用于计算天体物理模拟中辐射场（包括吸收）的通用算法。 TREVR旨在处理大量光源和吸收体；它基于树状数据结构，因此适用于使用树状结构进行引力或流体力学求解的代码（例如自适应网格细化）。 通过有控制地降低每个光源及其射线的分辨率，TREVR在保证指定精度的同时实现了计算速度的提升。 在无吸收的情况下，TREVR以 ${N\log N_{source}}$ 阶时间计算辐射场，在有吸收的情况下以 ${N \log N_{source} \log{N}}$ 阶时间计算。 这些标度源自根据开角准则合并辐射源，并遍历树状结构以追踪射线到达到选定吸收精度的深度。 吸收深度细化准则是TREVR独有的。 我们提供了一系列测试，展示了该算法准确计算通量、电离前沿和阴影的能力。 显示英文摘要

摘要： We present TREVR (Tree-based REVerse Ray Tracing), a general algorithm for computing the radiation field, including absorption, in astrophysical simulations. TREVR is designed to handle large numbers of sources and absorbers; it is based on a tree data structure and is thus suited to codes that use trees for their gravity or hydrodynamics solvers (e.g. Adaptive Mesh Refinement). It achieves computational speed while maintaining a specified accuracy via controlled lowering of the resolution of both sources and rays from each source. TREVR computes the radiation field in order ${N\log N_{source}}$ time without absorption and order ${N \log N_{source} \log{N}}$ time with absorption. These scalings arise from merging sources of radiation according to an opening angle criterion and walking the tree structure to trace a ray to a depth that gives the chosen accuracy for absorption. The absorption-depth refinement criterion is unique to TREVR. We provide a suite of tests demonstrating the algorithm's ability to accurately compute fluxes, ionization fronts and shadows.