I am new to processing and have been tinkering with the flock demo. I would like to repel the 'dots' with the mouse but am unsure as to how I should do this. I know I need to create a collision and have added an ellipse around the mouse but can not repel the dots successfully. Can anyone help?

The Dot is created in a seperate tab-

class Dot{ // define a new class

 float diameter;
 color c;

 PVector pos; // position
 PVector vel; // velocity
 PVector acc; // acceleration

 float mouseFactor = 0.05; // strength of mouse attraction //karen change from 0.1

 // cohesion variables
 float cohesionFactor = 0.05; //karen change from 0.2
 float cohesionRadius =  40;

 // alignment variables
 float alignFactor = 0.1;
 float alignRadius =  40;

 // separation variables
 float separationFactor = 10; // karen change from 1.5
 float separationRadius =  25; // karen change from 25

 // speed limit
 float maxVel = 2; //karen change from 5
 
 // friction
 float frictionFactor = 0.95;


 Dot(PVector _pos, float _diameter){ // constructor function has same name as class
   // constructor gets called when we make a new Dot
   pos = _pos;
   diameter = _diameter;
   vel = new PVector(random(-5,5),random(-5,5),0); // random initial velocity
   c = color(random(100,200),random(100,200),random(100,200)); // random initial colour //karen changed from 100-255 less pastel
   acc = new PVector(0,0,0); // set acceleration to 0
 }

 void run(){ // the main function - calls all the other behaviours and updates position and acceleration

     steerMouse(); // steer to mouse factor
   bounce();
   cohesion(); // cohesion factor, radius
   separation(); // separation factor, radius
   alignment();
   friction();
   speedLimit();

   render();

   vel.add(acc); // update the velocity vector - add the current acceleration vector
   pos.add(vel); // update the position - add the current velocity vector
   acc.mult(0); // reset acceleration to 0

 }

 void render(){ // draw the dot
   fill(c);
   ellipse(pos.x,pos.y,diameter,diameter);
 }



 void bounce(){
   if (pos.x > width || pos.x < 0){ // if x pos is greater than right hand edge OR less than left hand edge
     vel.set(vel.x*-1,vel.y,0); // bounce off the edge
   }
   if (pos.y > height || pos.y < 0) { // if y pos is greater than bottom edge OR less than top edge
     vel.set(vel.x,vel.y*-1,0);
   }

 }

 void steerMouse(){
   PVector mousePos = new PVector (mouseX,mouseY,0); // make a new vector based on the mouse position
   PVector toMouse = PVector.sub(mousePos,pos); // make a vector that point towards the mouse by subtracting vectors
   toMouse.normalize(); // scales the magnitude of the vector to 1
   toMouse.mult(mouseFactor); // multiplies the vector by the mouseFactor argument - which defines the strength of the mouse influence
   acc.add(toMouse); // add the toMouse force to our current acceleration
 }

 void separation(){
   for (int i=0; i<Dots.size(); i++){ // run through the arraylist
     Dot Neighbour = (Dot) Dots.get(i); // get each Dot
     float distance = PVector.dist(pos,Neighbour.pos);
     if (distance < separationRadius){ // if this Dot is within our separation range then
       PVector toNeighbour = PVector.sub(pos,Neighbour.pos); // make a vector from the neighbour
       toNeighbour.normalize(); // scale it to 1
       // now scale it according to distance, so that it's strong at close range, and reduces to 0 at the separation radius
       // then multiply it by the separationFactor, which allows us to control the overal strength of the separation force
       toNeighbour.mult(((separationRadius-distance)/separationRadius)*separationFactor
);
       acc.add(toNeighbour); // add the separation force to the acceleration
     }
   }
 }

 void cohesion(){ // each agent steers towards the average position of its neighbours
   PVector avePos = new PVector(); // PVector to store average position
   int neighbourcount = 0; // int to count the number of neighbours
   for (int i=0; i<Dots.size(); i++){
     Dot Neighbour = (Dot) Dots.get(i);
     float distance = PVector.dist(pos,Neighbour.pos);
     if (distance < cohesionRadius){
       avePos.add(Neighbour.pos);
       neighbourcount++;
     }
   }
   avePos.div(neighbourcount); // divide by num neighbours to get the average - the center position of our near neighbours
   PVector toCenter = PVector.sub(avePos,pos); // make a vector to that point
   toCenter.normalize(); // scale it to 1
   toCenter.mult(cohesionFactor); // multiply by cohesion factor
   acc.add(toCenter);    // add the cohesion force to the acceleration
 }


 void alignment(){
   PVector aveVel = new PVector(); // PVector to store average velocity of our neighbours
   for (int i=0; i<Dots.size(); i++){
     Dot Neighbour = (Dot) Dots.get(i);
     float distance = PVector.dist(pos,Neighbour.pos);
     if (distance < alignRadius){ // if the dot is within our alignment range
       aveVel.add(Neighbour.vel); // add its velocity to the average
     }
   }
   aveVel.normalize();
   aveVel.mult(alignFactor);
   acc.add(aveVel);  
 }


 void speedLimit(){
   if (vel.mag() > maxVel){ // if you're going faster than the speed limit
     vel.normalize(vel).mult(maxVel); // scale your velocity back to the limit
   }
 }

 void friction(){
   vel.mult(frictionFactor); // multiply velocity by the friction factor
 }

}



This is the primary tab


ArrayList Dots = new ArrayList();

void setup(){
 size(800,800);
 background(255);
 noStroke();
 smooth();
}
//add ellipse around mouse
void draw(){
 background(255);
 noFill();
 noStroke();
 ellipse(mouseX,mouseY,30,30);

 for (int i=0; i<Dots.size(); i++){ // step through the arraylist - size() gets the size of the arraylist
   Dot tempD = (Dot) Dots.get(i); // get an object out of the list, put it in

You can look at Keith Peters Actionscript 3 Animation book, it is all explain there and the code is easy to translate,

You can also have a look here
http://www.shiffman.net/teaching/nature/collisions/

Hope that helps
rS