Collective Behavior of Self Propelling Particles with Kinematic   Constraints; The relation between the discrete and the continuous description
  In two papers we proposed a continuum model for the dynamics of systems of self propelling particles with kinematic constraints on the velocities and discussed some of its properties. The model aims to be analogous to a discrete algorithm used in works by T. Vicsek et al. In this paper we derive the continuous hydrodynamic model from the discrete description. The similarities and differences between the resulting model and the hydrodynamic model postulated in our previous papers are discussed. The results clarify the assumptions used to obtain a continuous description. 
V.I. Ratushnaya, D. Bedeaux, V.L. Kulinskii, A.V. Zvelindovsky