/** * 400 particles are initialized with random positions and velocities.<br> * around each particle there is a repulsive zone between 30 and 50 pixels from it.<br> * other particles within that repulsive zone are pushed away in proprtion to the inverse of thier distance from that particle.<br> * a global compressive force pushes all particles toward the center in proportion to thier distance from the center. */ int num=400; //number of points float rf = 0.6; //strength of repulsive force float inner = 30; //inner boundary of repulsive zone in pixels float outer = 50; //outer boundary of repulsive zone in pixels float gpf = 0.001; //strength of global compressive force float fr = 0.9; //friction factor: multiplied by velocity each frame Part[] p = new Part[num]; void setup() { size(400, 400); smooth(); for(int i=0; i<num; i++) { p[i] = new Part(random(100,300),random(100,300),random(-0.0001,0.0001),random(-0.01,0.01)); } } void draw() { if (frameCount==1) background(0); fill(0,0,0,7); rect(0,0,width,height); noFill(); stroke(255); for(int i=0; i<num; i++) { p[i].calcvel(); p[i].move(); p[i].render(); } } class Part { public float px,py,vx,vy; Part(float PXA, float PYA, float VXA, float VYA) { px = PXA; py = PYA; vx = VXA; vy = VYA; } void calcvel() { float dx=0,dy=0,dis,rad,ax,ay; for(int i=0; i<num; i++) { if (p[i].px != px) { dx = p[i].px-px; dy = p[i].py-py; dis = sqrt(sq(dx)+sq(dy)); if (dis<outer && dis>inner) { rad = atan(dy/dx); ax = (1/dis)*cos(rad); ay = (1/dis)*sin(rad); if (dx > 0) ax *= -1; vx += rf*ax; vy += rf*ay; } } } vx += gpf*(200-px); vy += gpf*(200-py); vx *= fr; vy *= fr; if (abs(px-mouseX)<25 && abs(py-mouseY)<25 && mousePressed) { vx += random(-1,1); vy += random(-1,1); } } void move() { px += vx; py += vy; } void render() { point(px,py); } }

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This applet is about chaos and balance. I prefer to let it speak for itself. But I will offer a technical explanation.

400 particles are initialized with random positions and velocities. Around each particle there is a repulsive zone between 30 and 50 pixels from it. Other particles within that repulsive zone are pushed away in proportion to the inverse of their distance from that particle. A global compressive force pushes all particles toward the center in proportion to their distance from the center.

Nathan Nifong

http://uncc.ath.cx

2 Aug 2010