GRHayL: a modern, infrastructure-agnostic, extensible library for GRMHD simulations

TL;DR

GRHayL is a modular, extensible, and infrastructure-agnostic library for GRMHD simulations that facilitates verification, reuse, and rapid development across diverse high-performance computing platforms.

Contribution

It refactors IllinoisGRMHD into reusable kernels and demonstrates portability and validation across multiple frameworks, enhancing flexibility and verification in GRMHD simulations.

Findings

Comparable or improved behavior over legacy codes

Successful cross-infrastructure validation

Enhanced portability with minimal duplication

Abstract

Interpreting multimessenger signals from neutron stars and black holes requires reliable general relativistic magnetohydrodynamics (GRMHD) simulations across rapidly evolving high-performance computing platforms, yet key algorithms are routinely rewritten within infrastructure-specific numerical relativity codes, hindering verification and reuse. We present the General Relativistic Hydrodynamics Library (GRHayL), a modular, infrastructure-agnostic GR(M)HD library providing conservative-to-primitive recovery, reconstruction, flux/source and induction operators, equations of state, and neutrino leakage through an intuitive interface. GRHayL refactors and extends the mature IllinoisGRMHD code into reusable point- and stencilwise kernels, enabling rapid development and cross-code validation in diverse frameworks, while easing adoption of new microphysics and future accelerators. We implement the same kernels in the Einstein Toolkit (Carpet and Carpetx) and BlackHoles@Home, demonstrating portability with minimal duplication. Validation combines continuous-integration unit tests with cross-infrastructure comparisons of analytic GRMHD Riemann problems, dynamical Tolman-Oppenheimer-Volkoff evolutions, and binary neutron star mergers, showing comparable or improved behavior over legacy IllinoisGRMHD and established Einstein Toolkit codes.