def nu_to_D(nu): """Parabolic eccentric anomaly from true anomaly. Parameters ---------- nu : ~astropy.units.Quantity True anomaly. Returns ------- D : ~astropy.units.Quantity Hyperbolic eccentric anomaly. Notes ----- Taken from Farnocchia, Davide, Davide Bracali Cioci, and Andrea Milani. "Robust resolution of Kepler’s equation in all eccentricity regimes." Celestial Mechanics and Dynamical Astronomy 116, no. 1 (2013): 21-34. """ return (nu_to_D_fast(nu.to(u.rad).value) * u.rad).to(nu.unit)