Effect of attractive interaction on instability of pedestrian flow in a two-dimensional optimal velocity model.

We incorporate an attractive interaction in a two-dimensional optimal velocity model and investigate the stability of homogeneous flow in the linear approximation. There exists a different type of instability in this model. We show the phase diagram and the behavior of the flow in each phase by numerical simulations. A new phase due to the new instability appears at low density, and the instability can be a candidate of the group formation mechanism of organisms.