The Kratos Framework for Heterogeneous Astrophysical Simulations: Ray Tracing, Reacting Flow and Thermochemistry

Thermochemistry, ray-tracing radiation, and radiation-matter interactions are important processes which are computationally difficult to model in astrophysical simulations, addressed by introducing novel algorithms optimized for heterogeneous architectures in the Kratos framework. Key innovations include a stoichiometry-compatible reconstruction scheme for consistent chemical species advection, which ensures element conservation while avoiding matrix inversions, and a LU decomposition method specifically designed for multi-thread parallelization in order to solve stiff thermochemical ordinary differential equations with high efficiency. The framework also implements efficient ray-tracing techniques for radiation transport for radiation-matter interactions. Various verification tests, spanning from chemical advection, combustion, Str\"omgren spheres, and detonation dynamics, are conducted to demonstrate the accuracy and robustness of Kratos, with results closely matching semi-analytic solutions and benchmarks such as Cantera and the Shock and Detonation Toolbox. The modular design and performance optimizations position it as a versatile tool for studying coupled microphysical processes in the diverse environments of contemporary astrophysical studies.