Jx: An open-source software for calculating magnetic interactions based on magnetic force theory

We describe our newly-developed open-source software, named by J_x, to perform magnetic force linear response calculations. J_x is a user-friendly and efficient tool to calculate magnetic interaction in solids and molecules. Without supercell calculation, it computes both short- and long-range interactions. It is also possible to calculate an orbital-resolved matrix form of magnetic couplings. Functionality and formalism are presented with examples. The program architecture and parallel algorithm are also described.