Boris Daszuta (Friedrich-Schiller-Universität Jena)

`GR-Athena++` is a general-relativistic, high-order, vertex-centered solver that extends the oct-tree, adaptive mesh refinement capabilities of the astrophysical (radiation) magnetohydrodynamics code `Athena++`. To simulate dynamical spacetimes `GR-Athena++` uses the Z4c evolution scheme of numerical relativity coupled to the moving puncture gauge. Stable and accurate binary black hole merger evolutions are demonstrated in convergence testing, cross-code validation, and verification against state-of-the-art effective-one-body waveforms. `GR-Athena++` leverages the task-based parallelism paradigm of `Athena++` to achieve excellent scalability. Strong scaling efficiencies above 95% for up to 1.2×1e4 CPUs and excellent weak scaling up to 1e5 CPUs in a production binary black hole setup with adaptive mesh refinement are measured. `GR-Athena++` thus allows for the robust simulation of compact binary coalescences and and offers a viable path towards numerical relativity at exascale.

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