Flash ActionScript 3.0: Number Type and Decimal Precision (Vector Fields and Particles)

Question

I simulate a vector field in a flash and create a mess of particles to visualize the flow of the field. Using the vector field F (x, y) = yi-xj

This vector field has a curl, the particles must move in the circles that they perform. My problem is that the particles diverge from the origin, although this particular vector field has no divergence. I suspect that my data types may lose decimal precision during the most basic cases for this field, or perhaps I am mistaken in a logical error. I'm not sure.

This code produces particles on the screen (this is 800x450). This code is probably not in trouble, but for completeness I have included it.

//spawn particles
var i:int;
var j:int;
//spread is the spacing between particles
var spread:Number;
spread = 10.0;
//spawn the particles
for (i=0; i<=800/spread; i++)
{
 for (j=0; j<=450/spread; j++)
 {
  //computes the particles position and then constructs the particle.
  var iPos:Number = spread * Number(i) - 400.0;
  var jPos:Number = 225.0 - spread * Number(j);
  var particle:dot = new dot(iPos,jPos,10.0);
  addChild(particle);
 }
}

This is the point class, which contains everything that is important for the generated particles.

package 
{
 //import stuff
 import flash.display.MovieClip;
 import flash.events.Event;
 public class dot extends MovieClip
 {
  //variables
  private var xPos:Number;
  private var yPos:Number;
  private var xVel:Number;
  private var yVel:Number;
  private var mass:Number;
  //constructor
  public function dot(xPos:Number, yPos:Number, mass:Number)
  {
   //Defines the function to be called when the stage advances a frame.
   this.addEventListener(Event.ENTER_FRAME, moveDot);
   //Sets variables from the constructor arguments.
   this.xPos = xPos;
   this.yPos = yPos;
   this.mass = mass;
   //Set these equal to 0.0 so the Number type knows I want a decimal (hopefully).
   xVel = 0.0;
   yVel = 0.0;
  }
  //Controlls the particle behavior when the stage advances a frame.
  private function moveDot(event:Event)
  {
   //The vector field is a force field. F=ma, so we add F/m to the velocity. The mass acts as a time dampener.
   xVel += yPos / mass;
   yVel +=  -  xPos / mass;
   //Add the velocity to the cartesian coordinates.
   xPos +=  xVel;
   yPos +=  yVel;
   //Convert the cartesian coordinates to the stage native coordinates.
   this.x = xPos + 400.0;
   this.y = 225.0 + yPos;
  }
 }
}

. , , . . !

Answer 1

(, ). , - ENTER_FRAME , 3600. . .

Answer 2

toFixed().

//Set these equal to 0.0 so the Number type knows I want a decimal (hopefully).
 xVel = 0;
 yVel = 0;
 xVel.toFixed(1); //(specifies decimal places)
 yVel.toFixed(1);

Hope this helps