  Considering systems of self-propelled polar particles with nematic
interactions ("rods"), we compare the continuum equations describing the
evolution of polar and nematic order parameters, derived either from
Smoluchowski or Boltzmann equations. Our main goal is to understand the
discrepancies between the continuum equations obtained so far in both
frameworks. We first show that in the simple case of point-like particles with
only alignment interactions, the continuum equations obtained have the same
structure in both cases. We further study, in the Smoluchowski framework, the
case where an interaction force is added on top of the aligning torque. This
clarifies the origin of the additional terms obtained in previous works. Our
observations lead us to emphasize the need for a more involved closure scheme
than the standard normal form of the distribution when dealing with active
systems.
