GPU Accelerated INtensities MPI (GAIN-MPI): A new method of computing Einstein-A coefficients

Calculating dipole transition intensities or the related Einstein A coefficients can dominate the computer usage for large line lists of transitions such as those being computed to model radiative transport through hot atmospheres. An algorithm for the efficient computation of line strengths is presented based on the use of the half-linestrength. This is implemented on GPUs, are shown to give up to a thousandfold speed-up compared to calculations on conventional computers. This algorithm is implemented in the program GAIN which was developed as part of the TROVE nuclear motion program, but can be adapted for use by other similar programs in a straightforward fashion.