EXP: a Python/C++ package for basis function expansion methods in galactic dynamics

Galaxies are ensembles of dark and baryonic matter confined by their mutual gravitational attraction.The dynamics of galactic evolution have been studied with a combination of numerical simulations and analytical methods (Binney & Tremaine, 2008) for decades.Recently, data describing the positions and motions of billions of stars from the Gaia satellite (Gaia Collaboration, 2016, 2018) depict a Milky Way (our home galaxy) much farther from equilibrium than we imagined and beyond the range of many analytic models.Simulations that allow collections of bodies to evolve under their mutual gravity are capable of reproducing such complexities but robust links to fundamental theoretical explanations are still missing.