pint.orbital.kepler.kepler_2d

pint.orbital.kepler.kepler_2d(params, t)

Position and velocity of a particle in a Kepler orbit.

The orbit has semi-major axis a, period pb, and eccentricity parametrized by eps1=e*sin(om) and eps2=e*cos(om), and the particle is on the x axis at time t0, while the values are computed for time t.

The function returns a pair (xv, p), where xv is of length four and consists of (x,y,v_x,v_y), and p is of shape (4,5) and cell (i,j) contains the the partial derivative of the ith element of xv with respect to the jth orbital parameter.

The zero of time is when the particle is on the positive x axis. (Which will be the ascending node in a three-dimensional model.)