def METHOD_NAME(x, params):
    """ Isochrone Hamiltonian = -GM/(b+sqrt(b**2+(r-r0)**2))"""
    #r = (np.sqrt(np.sum(x[:3]**2))-params[2])**2
    r = np.sum(x[:3]**2)
    return 0.5*np.sum(x[3:]**2)-Grav*params[0]/(params[1]+np.sqrt(params[1]**2+r))