Dancing with friends and enemies: boids' swarm intelligence

Adapted from Wolfram Community. Written by Simon Woods

1000 dancers assume random positions on the dance-floor.
Each randomly chooses one "friend" and one "enemy".
At each step every dancer
- moves 0.5% closer to the centre of the floor
- then takes a large step towards their friend and a small step away from their enemy.
At random intervals one dancer re-chooses their friend and enemy

Randomness is deliberately injected. Here is the dance...

Evaluate initialization cells first

or go one by one

n = 1000;
r := RandomInteger[{1, n}];
f := (#/(.01 + Sqrt[#.#])) & /@ (x[[#]] - x) &;
s := With[{r1 = r}, p[[r1]] = r; q[[r1]] = r];
x = RandomReal[{-1, 1}, {n, 2}];
{p, q} = RandomInteger[{1, n}, {2, n}];

Main render function

EventHandler["frame", Function[Null,
  x = 0.995 x + 0.02 f[p] - 0.01 f[q];
  If[r < 100, s];
]];

Drawing function Evaluate this cell very last

Graphics[{
  PointSize[0.007], Point[x // Offload],
  AnimationFrameListener[x // Offload, "Event"->"frame"]
}, PlotRange -> {{-2,2}, {-2,2}}, TransitionType->None]  

(*VB[*)(FrontEndRef["c2a108dd-d7c9-4f48-8ad8-8445b67ed254"])(*,*)(*"1:eJxTTMoPSmNkYGAoZgESHvk5KRCeEJBwK8rPK3HNS3GtSE0uLUlMykkNVgEKJxslGhpYpKToppgnW+qapJlY6FokpgAJExPTJDPz1BQjUxMAiq4VtA=="*)(*]VB*)

To stop

EventRemove["frame"];

To restart - evaluate EventHandler and then a kick-starter

EventFire["frame", Null];