# Craig Reynolds: boids flock

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Exploring Everyday Things with R and Ruby by Sau Sheong Chang

While not as spectacular as the starling swarms in Europe, which often number in the hundreds of thousands and are sometimes referred to as the “Black Sun,” the mynah swarms are interesting enough to start a train of thought that has eventually led me to this basic question: how and why do these birds flock the way they do? As usual, I started off my quest with some searches on trusty old Google, which brought up a number of intriguing results. As it turns out, there is a whole bunch of existing research on flocking birds and swarming insects, dating back to more than 30 years ago. One popular and well-known product of this research is the Boids algorithm created by Craig Reynolds in 1986. The Origin of Boids Boids is an artificial life program developed by Craig Reynolds to simulate the behavior of flocking birds. The name refers to the birdlike objects that populate the simulation.

The radii for the align and cohere rules are relatively larger, as we want the roids to collect in a single group rather than many small groups. There you have it—these three rules make up the original Boids flocking algorithm created by Craig Reynolds. Supporting Rules While Reynolds’s three rules suffice to make a rather compelling simulation, we need a couple more rules to make the simulation run smoothly: Muffle the speed of the roid. We don’t want roids to randomly speed up as a result of flocking. Real birds can’t speed up too much, so we must slow down the roids if they move too fast as a result of our flocking rules. Allow the roid to fall through from one side of the application window into the other.

pages: 247 words: 43,430

Think Complexity by Allen B. Downey

Heterogeneity What if all drivers are not the same; for example, what if they have different speed limits or following distances? Boids In 1987, Craig Reynolds published “Flocks, herds, and schools: A distributed behavioral model,” which describes an agent-based model of herd behavior. You can download his paper from http://www.red3d.com/cwr/papers/1987/boids.html. Agents in this models are called “boids,” which is both a contraction of “bird-oid” and an accented pronunciation of “bird” (although boids are also used to model fish and herding land animals). Each agent simulates three behaviors: Collision avoidance Avoid obstacles, including other birds. Flock centering Move toward the center of the flock. Velocity matching Align velocity with neighboring birds.

Many parameters influence flock behavior, including the range, angle, and weight for each behavior, and the maneuverability, mu. These parameters determine the ability of the boids to form and maintain a flock, and the patterns of motion and organization in the flock. For some settings, the boids resemble a flock of birds; other settings resemble a school of fish or a cloud of flying insects. Example 10-4. Run my implementation of the boid algorithm, and experiment with different parameters. What happens if you “turn off” one of the behaviors by setting the weight to 0? To generate more bird-like behavior, Flake suggests adding a fourth behavior to maintain a clear line of sight; in other words, if there is another boid directly ahead, the boid should move away laterally.

Velocity matching Align velocity with neighboring birds. Boids make decisions based on local information only; each boid only sees (or pays attention to) other boids in its field of vision and range. The Visual package, also known as VPython, is well suited for implementing boids. It provides simple 3D graphics as well as vector objects and operations that are useful for the computations. You can download my implementation from http://thinkcomplex.com/Boids.py. It is based in part on the description of boids in Flake’s The Computational Beauty of Nature. The program defines two classes: Boid, which implements the boid algorithm, and World, which contains a list of boids and a “carrot” the boids are attracted to.

pages: 293 words: 88,490

The End of Theory: Financial Crises, the Failure of Economics, and the Sweep of Human Interaction by Richard Bookstaber

Yet the task turns out to be remarkably easy if it is viewed, more realistically, as the aggregation of local interactions by the individual birds in the flock. In an early simulation of that emergent phenomenon, Craig Reynolds, a software engineer and Academy Award winner,3 built a dynamic model for a flock of artificial “boids” based on three simple rules: 1. Separation: don’t get too close to any object, including other boids. 2. Alignment: try to match the speed and direction of nearby boids. 3. Cohesion: head for the perceived center of mass of the boids in your immediate neighborhood. Boids can be structured as a cellular automaton along the lines of Life, with each boid seeing only its immediate surroundings and acting based on simple rules.

If you read the accounts by those who were in the middle of, say, the Bear Stearns implosion, the observations and actions don’t follow some model. The accounts are about stressed-out people packed around a table trying to puzzle out what’s going on and devise the best course of action As an example of the difference between focusing on dynamic interactions based on heuristics and a general model, let’s go back to the boids of chapter 3—modeling birds in flight. How do we explain the ability of birds to fly in V formations? A model consistent with the neoclassical approach would determine a utility function to optimize the effort and speed of the birds, dealing with the dynamics of flight. This will lead to a complex mathematical problem that can be the fodder for all sorts of follow-on manipulations.

pages: 294 words: 82,438

Simple Rules: How to Thrive in a Complex World by Donald Sull, Kathleen M. Eisenhardt

Reynolds created avian avatars, which he dubbed “boids,” and wrote a software program in which each boid followed three simple rules based on the position and behavior of nearby flock mates. The three rules are: (1) avoid collisions, (2) head in the same direction as your nearest neighbors, and (3) stay close to your nearest neighbors. These three rules are all that boids need to coordinate with one another and produce their amazing group-level flocking behavior, closely matching that of real birds. Behavioral biologists, who tested Reynolds’s rules in the wild, found that they could explain collective behavior in a wide range of settings, including how mosquitofish shoal, starlings flock, and pedestrians self-organize into orderly lines on busy streets.

Fellow ornithologists wisely dismissed thought-transference but could not come up with a better explanation of flocking behavior. For fifty years after Selous published his book, the question of how starlings orchestrated a murmuration remained unanswered. The solution to how starlings flock came unexpectedly from a software engineer working in a computer lab, not from an ornithologist traipsing around a field. Craig Reynolds studied at MIT, where he wrote his bachelor’s and master’s theses on computer animation. While designing computer-graphics software, Reynolds grew interested in how to simulate coordinated activity in animals, such as the flocking of birds. Reynolds created avian avatars, which he dubbed “boids,” and wrote a software program in which each boid followed three simple rules based on the position and behavior of nearby flock mates.

. [>] Reynolds created avian: Craig Reynolds, “Flocks, Herds, and Schools: A Distributed Behavioral Model,” Computer Graphics 21 (1987): 25–34. [>] Behavioral biologists: Ballerini et al. review the models of collective animal behavior and summarize that all agree on three behavioral rules: “move in the same direction as your neighbors, remain close to them, avoid collisions.” Michele Ballerini et al., “Interaction Ruling Animal Collective Behaviour Depends on Topological Rather than Metric Distance: Evidence From a Field Study,” Proceedings of the National Academy of Science USA 105 (2008): 1232–37. [>] In flocks, however: C.

The Greatest Show on Earth: The Evidence for Evolution by Richard Dawkins

If you’ve got the behavioural rules right for a single starling, a thousand computer starlings, each one a dot on the screen, will behave like real starlings flocking in winter. If the flocking behaviour isn’t quite right, you can go back and adjust the behaviour of the individual starling, perhaps in the light of further measurements of the behaviour of real starlings. Now clone up the new version a thousand times, in place of the thousand that didn’t quite work. Keep iterating your reprogramming of the cloned-up single starling, until the flocking behaviour of thousands of them on the screen is a satisfyingly realistic screensaver. Calling it ‘Boids’, Craig Reynolds wrote a program along these lines (not specifically for starlings) in 1986. The key point is that there is no choreographer and no leader.

‘All things dull and ugly’: lyrics reproduced with thanks by permission of Python (Monty) Pictures. Thanks to Terry Jones and Eric Idle. p. 218 There are some stunning films available on YouTube: For example, http://www.youtube.com/watch?v=XH-groCeKbE. pp. 219–20 Calling it ‘Boids’, Craig Reynolds wrote a program along these lines: http://www.red3d.com/cwr/boids/. p. 229 it has been deciphered by a group of scientists associated with the brilliant mathematical biologist George Oster: Odell et al. (1980). p. 233 An early classic experiment by the Nobel Prize-winning embryologist Roger Sperry: Meyer (1998). p. 243 the complete family tree of all 558 cells of a newly hatched larva: C. elegans cell family tree from www.wormatlas.org/userguides.html/lineage.htm.

That is just as well for, given the speed at which they fly, any such impact would severely injure them. Often the whole flock seems to behave as a single individual, wheeling and turning as one. It can look as though the separate flocks are moving through each other in opposite directions, maintaining their coherence intact as separate flocks. This makes it seem almost miraculous, but actually the flocks are at different distances from the camera and do not literally move through each other. It adds to the aesthetic pleasure that the edges of the flocks are so sharply defined. They don’t peter off gradually, but come to an abrupt boundary.

pages: 797 words: 227,399

Wired for War: The Robotics Revolution and Conflict in the 21st Century by P. W. Singer

As one army colonel asked, “Obviously the birds lack published doctrine and are not receiving instructions from their flight leader, so how can they accomplish the kind of self-organization necessary for flocking?” The answer actually comes from a researcher, Craig Reynolds, who built a program for what he called “boids,” artificial birds. As an army report on the experience described, all the boids needed to do to organize themselves together as a flock was for each individual boid to follow three simple rules: “1. Separation: Don’t get too close to any object, including other boids. 2. Alignment: Try to match the speed and direction of nearby boids. 3. Cohesion: Head for the perceived center of mass of the boids in your immediate neighborhood.” This basic boid system worked so well that it was also used in the movie Batman Returns, to create the realistic-looking bat sequences.

The U.S. military hopes to do this by building what it calls “an unassailable wireless ‘Internet in the sky.’ ” Basically, it plans to take the kind of wireless network you might use at Starbucks and make it global by beaming it off of satellites, so a robot anywhere in the world could hook into and share information instantaneously. Of course, others think that this will make U.S. military doctrine inherently vulnerable to computer hacking, or even worse. As one military researcher put it, “They should just go ahead and call it Skynet.” Just as the birds and the boids follow very simple rules to carry out very complex operations, so would an unmanned swarm in war. Each system would be given a few operating orders and let loose, each robot acting on its own, but also in collaboration with all the others. The direction of the swarm could be roughly guided by giving the robots a series of objectives ranked in priority, such as a list of targets given point value rankings.

Fabey, “F-22: Unseen and Lethal,” Aviation Week & Space Technology 166, no. 2 (2007): 46. 230 “If you look at nature’s most efficient predators” Noah Shachtman, as quoted in Warbots, History Channel, broadcast on August 8, 2006. 231 40 percent of these victories Sean J. A. Edwards, “Swarming and the Future of Warfare” (doctoral thesis, Pardee Rand Graduate School, 2005), 83. 231 “an influence, a thing invulnerable, intangible” Ibid., 64. 231 “Obviously the birds lack” Thomas K. Adams, “The Real Military Revolution,” Parameters 30, no. 3 (2000). 231 “boids,” artificial birds Craig W. Reynolds, “An Evolved, Vision-Based Model of Obstacle Avoidance Behavior,” in Proceedings, ed. C. Langton (Redwood City, CA: Addison-Wesley, 1994). 231 follow three simple rules Adams, “The Real Military Revolution.” 232 “the wisdom of crowds” James Surowiecki, The Wisdom of Crowds: Why the Many Are Smarter than the Few and How Collective Wisdom Shapes Business, Economies, Societies, and Nations, 1st ed.

pages: 402 words: 110,972

Nerds on Wall Street: Math, Machines and Wired Markets by David J. Leinweber

But giving them a few simple rules, like “fly toward the closest bird,” “go with the flow,” and “don’t hit other birds,” could give rise to distinctly birdlike behavior. The original ALife flock is Craig Reynolds’ “Boids,” done at Symbolics in 1986.† Simulated herding and flocking turn out to be of some commercial interest. Those massive stampedes in Disney cartoons, with thousands of <insert fast, large mammal of your choice>, and all those schools of talking fish are descendants of the Boids. Hollywood showed its appreciation by giving Reynolds an Academy Award in 1998. *“The Santa Fe Institute is devoted to creating a new kind of scientific research community, one emphasizing multidisciplinary collaboration in pursuit of understanding the common themes that arise in natural, artificial, and social systems.”

*“The Santa Fe Institute is devoted to creating a new kind of scientific research community, one emphasizing multidisciplinary collaboration in pursuit of understanding the common themes that arise in natural, artificial, and social systems.” It was founded in 1984 (www.santafe.edu/). † . . . and still flocking after all these years at www.red3d.com/cwr/boids. 156 Nerds on Wall Str eet Like our early algos, the SFI artificial life was dumb, just obeying a few simple handwritten rules, without any ability to learn from mistakes. But the ALife researchers had a good answer—evolving intelligent behavior by mimicking natural evolution. Represent the programs as digital chromosomes, and simulate crossover and mutation, to breed better programs.

pages: 287 words: 86,919

Protocol: how control exists after decentralization by Alexander R. Galloway

He writes: “I proposed to create a very large, complex and inter-connected region of cyberspace that will be inoculated with digital organisms which will be allowed to evolve freely through natural selection”94—the goal of which is to model the 92. For other examples of artiﬁcial life computer systems, see Craig Reynolds’s “boids” and the ﬂocking algorithm that governs their behavior, Larry Yaeger’s “Polyworld,” Myron Krüger’s “Critter,” John Conway’s “Game of Life,” and others. 93. Tom Ray, “What Tierra Is,” available online at http://www.hip.atr.co.jp/~ray/tierra/ whatis.html. 94. Tom Ray, “Beyond Tierra: Towards the Digital Wildlife Reserve,” available online at http://www1.univap.br/~pedrob/PAPERS/FSP_96/APRIL_07/tom_ray/node5.html.

“We believe in freedom of speech, the right to explore and learn by doing, and the tremendous power of the individual.”30 Yet this is a new type of individual. This is not the same individual who is the subject of enlightenment liberalism. It is an extension (perhaps) of the modern dream of individuality and independence. Yet this new resistive agent has more in common with the autonomous “boids” of Tom Ray’s Tierra than with radicals from protocol’s prehistory. “A true hacker is not a group person,”31 wrote Stewart Brand in 1972. Or, as he would write ﬁfteen years later: “Workers of the world, fan out”32—advice that inverts the message of resistance-through-unity found in Marx and Engel’s Communist Manifesto.