vector getSpringForce(position from,position to,float desiredLength,float constant)
{
  vector force=new vector(from,to);
  float distance=dist(from,to);
  if(distance!=0)
  {
    vector deltaLength;
//    float delta=(distance-desiredLength);    
//    force.m=delta;
//    position targetPos=new position(force.ep());
    position targetPos;
    if(useRK)    
      targetPos=new position(to.displaceRK(force.a+180,desiredLength));
    else
      targetPos=new position(to.displace(force.a+180,desiredLength));    
//    position targetPos=new position(to.displace(getHeading(to,from),desiredLength));    
    deltaLength=new vector(from,targetPos);
//    fill(255,0,0);
//    ellipse(targetPos.x,targetPos.y,5,5);
    force=new vector(deltaLength);
    force.m*=constant;
//    force.m=constrain(force.m,-50,50);
  }
  return force;
}

float getSpringForceScalar(float from,float to,float desiredLength,float constant)
{
  float force=to;
  force-=from;
  if(force!=0)
  {
    float deltaLength=force;
    float targetLength=desiredLength;
    deltaLength=deltaLength-targetLength;
    force=deltaLength;
    force*=constant;
  }

  return force;
}