<tt>MHDuet</tt> : a high-order general relativistic radiation MHD code for CPU and GPU architectures

Abstract We present MHDuet , an open source evolution code for general relativistic magnetohydrodynamics with neutrino transport. The code solves the full set of Einstein equations coupled to a relativistic, magnetized fluid with an M1 neutrino radiation scheme using advanced techniques, including adaptive mesh and large eddy simulation techniques, to achieve high accuracy. The Simflowny platform generates the code from a high-level specification of the computational system, producing code that runs with either the structured adaptive mesh refinement application infrastructure (SAMRAI) or adaptive mesh refinement framework for exascale computing (AMReX) infrastructure. The choice of AMReX enables compilation and execution on graphical processing units, running an order of magnitude faster than on central processing units at the node level. We validate the code against benchmark tests, reproducing previous results obtained with the SAMRAI infrastructure, and demonstrate its capabilities with simulations of neutron stars employing realistic tabulated equations of state. Resolution studies clearly demonstrate convergence faster than second order in the grid spacing. Scaling tests reveal excellent strong and weak scaling performance when running on graphical processing units. The goal of the code is to provide a powerful tool for studying the dynamics of compact objects within multi-messenger astrophysics.