gyre: an open-source stellar oscillation code based on a new Magnus Multiple Shooting scheme

We present a new oscillation code, gyre, which solves the stellar pulsation equations (both adiabatic and non-adiabatic) using a novel Magnus Multiple Shooting numerical scheme devised to overcome certain weaknesses of the usual relaxation and shooting schemes appearing in the literature. The code is accurate (up to sixth-order in the number of grid points), robust, efficiently makes use of multiple processor cores and/or nodes and is freely available in source form for use and distribution. We verify the code against analytic solutions and results from other oscillation codes, in all cases finding good agreement. Then, we use the code to explore how the asteroseismic observables of a 1.5 M-circle dot star change as it evolves through the red-giant bump.