Computational performance versus numerical accuracy in the acoustic terms of weakly-compressible SPH
Accurate computation of the acoustic terms in weakly-compressible SPH, including the equation of state, its inverse, and the evaluation of the local speed of sound, is essential to ensure energy conservation, robust solid boundary conditions, and correct open boundary behavior. In the classic Cole's equation of state, using values of the polytropic constant $γ\ne 1$ can lead to significant precision loss, particularly when computations are performed in single precision, as is common in GPU implementations. We extend here our previous results on the optimal choice of state variable by introducing a new higher-precision form for all three acoustic terms, denoted \texttt{explog}, and assess its numerical accuracy and computational performance across a variety of devices and test cases. We find that the new form evaluates the acoustic terms with a maximum ULP of~2 for arguments less than $0.125$, and has higher errors in less than 1\% of the arguments larger than the threshold. Combined with a rewritten expression of the pressure at solid boundary particles in the ``dummy'' model, it provides consistently more accurate results, maintaining deviations from the reference pressure profile to below 2\%, even in presence of a rough bottom terrain. Computationally, the new formulation is also faster than the naive one on GPU, and only marginally slower on CPU.