Talk:Vicsek model

Greetings,

I am writing about the mathematical notation used to describe $\Theta _{i}(t+\Delta t)$. Though one can guess that the individual's direction of motion is a function of his neighbor's directions, I am not sure what the bracket notation of the term $\langle \Theta _{j}\rangle _{|r_{i}-r_{j}|<r}$ means - is it an average? A linear Combination? A non-linear function? Any function? Furthermore, is that notation standard?