N-Body Gravitation

Here is a function for animating the n-body gravitational force between bodies:

public function animate(planetA:Array):void{
 
			var len:int = planetA.length;
 
			for(var k:int=0; k<len; k++){
 
				var p:Planet = planetA[k];
 
				for(var m:int=k+1; m<len; m++){
 
				var q:Planet = planetA[m];
 
				var a = q.scaling/(Math.pow(p.xo - q.xo, 2) + Math.pow(p.yo - q.yo, 2));
				var theta = Math.atan2(q.yo - p.yo, q.xo - p.xo);
				p.ax = a*Math.cos(theta);
				p.ay = a*Math.sin(theta);
				p.vx += p.ax;
				p.vy += p.ay;
				p.xo += p.vx;
				p.yo += p.vy;
 
 
 
				}
 
 
				if(p.xo>800||p.xo<0||p.yo>800||p.yo<0){
					planetA.splice(k, 1);
					len--;
				}
 
				this.graphics.drawCircle(p.xo, p.yo, p.scaling/20);
 
			}
 
		}

class Planet extends Sprite{
 
				public var scaling:Number = Math.random()*100 + 50;
				public var vx:Number = (Math.random()*1)-0.5;
				public var vy:Number = (Math.random()*1)-0.5;
				public var ax:Number = 0;
				public var ay:Number = 0;
				public var xo:Number = 0;
				public var yo:Number = 0;
 
				public function Planet():void{
					this.graphics.beginFill(0xcc0000, 1);
					this.graphics.drawCircle(0,0,scaling);
					this.graphics.endFill();
				}
 
		}