Editing Flocking (section)

=== Reynolds' Models ===
Flocking behaviour was simulated on a computer in 1987 by [[Craig Reynolds (computer graphics)|Craig Reynolds]] with the program [[Boids]].<ref>{{cite conference
|author= Reynolds, Craig W.
|title= Flocks, herds and schools: A distributed behavioural model.
|book-title= ACM SIGGRAPH Computer Graphics
|volume=21 |issue=4 |pages= 25–34
|year=1987
}}</ref> This program simulates simple agents (boids) that move according to a set of three basic rules: separation, alignment and cohesion. The result, akin to a [[Flock (birds)|flock]] of [[bird]]s, a [[Shoaling and schooling|school]] of [[fish]], or a [[swarm]] of [[insects]], was developed for motion picture visual effects.

==== Rules ====

Reynolds' models of flocking behaviour are controlled by three simple rules:

;Separation
:Avoid crowding neighbours (short range repulsion)
;Alignment 
:Steer towards average heading of neighbours
;Cohesion 
:Steer towards average position of neighbours (long range attraction)

With these three simple rules, the flock moves in an extremely realistic way, creating complex motion and interaction that would be extremely hard to create otherwise.

==== Rule variants ====

The basic model has been extended in several different ways since Reynolds proposed it. For instance, Delgado-Mata et al.<ref>{{Cite journal |display-authors=etal |vauthors=Delgado-Mata C, Ibanez J, Bee S |year=2007 |title=On the use of Virtual Animals with Artificial Fear in Virtual Environments |journal=New Generation Computing |volume=25 |issue=2 |pages=145–169 |doi=10.1007/s00354-007-0009-5 |s2cid=26078361}}</ref> extended the basic model to incorporate the effects of fear. Olfaction was used to transmit emotion between animals, through pheromones modelled as particles in a free expansion gas.

Hartman and Benes<ref>{{Cite journal |vauthors=Hartman C, Benes B |year=2006 |title=Autonomous boids | journal=Computer Animation and Virtual Worlds |volume=17 |issue=3–4 |pages=199–206 |doi=10.1002/cav.123 |s2cid=15720643}}</ref> introduced a complementary force to the alignment that they call the change of leadership. This steer defines the chance of the bird to become a leader and try to escape.