NetLogo User Community Models

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Download If clicking does not initiate a download, try right clicking or control clicking and choosing "Save" or "Download".(The run link is disabled because this model's memory requirements are too large.)

WHAT IS IT?

This model is a replication of the one developed by Iain D. Couzin, Jens Krause, Nigel R. Franks & Simon A. Levin (2005, Nature). Using rules of flocking in birds and schools of fish, the model shows how group members take a collective decision to move in the direction of a food location, even if only few individuals know where this location is. Other group members do not know which individuals have the information, but the group stay cohesive and move toward the food location.

I have used the model 'flocking' of Wilensky (1998) for the processes of collective movements of animals.
Animals follow three rules: "alignment", "separation", and "cohesion". "Alignment" means that an individual tends to turn so that it is moving in the same direction that nearby animals are moving. "Separation" means that an individual will turn to avoid another bird which gets too close. "Cohesion" means that an individual will move towards other nearby individuals (unless another bird is too close). When two animals are too close, the "separation" rule overrides the other two, which are deactivated until the minimum separation is achieved.

The three rules affect only the animal's heading. Each individual always moves forward at the same constant speed.

HOW TO USE IT

Determine the number of individuals (population) you want in the simulation and set the POPULATION slider to that value. Press SETUP to create individuals,
Create a patch (one pixel) to determine the direction to move.
You can create another patch (second button) to create another group of informed individuals, i.e. two groups wanting to move in two different directions.

press GO to have them start moving around.

The default settings for the sliders will produce reasonably good flocking behavior. However, you can play with them to get variations:

Three TURN-ANGLE sliders control the maximum angle a bird can turn as a result of each rule.

VISION is the distance that each bird can see 360 degrees around it.

CREDITS AND REFERENCES

This model is inspired by Couzin et al. (2005), Wilensky (1998) and the Boids simulation invented by Craig Reynolds. The algorithm we use here is roughly similar to the original Boids algorithm, but it is not the same. The exact details of the algorithm tend not to matter very much -- as long as you have alignment, separation, and cohesion, you will usually get flocking behavior resembling that produced by Reynolds' original model. Information on Boids is available at http://www.red3d.com/cwr/boids/.

Couzin, I.D., Krause , J., Franks, N.R. & Levin, S.A., 2005. Effective leadership and decision-making in animal groups on the move. Nature, 433, 513-516. (doi: 10.1038/nature03236)

Model by Sueur Cédric.
http://cedric.sueur1.free.fr/home.html