code: def spin_in_roche(s, etheta, elongan, eincl):
    
    #  m = Rz(long).Rx(-incl).Rz(theta).Rz(pi)
    m = euler_trans_matrix(etheta, elongan, eincl)
  
    return np.dot(m.T, s)
docs: Transform the spin s of a star on Kerpler orbit with
  
        etheta  - true anomaly
        elongan - longitude of ascending node
        eincl - inclination
  
      from in the plane of sky reference frame into
      the Roche reference frame.