4 (
double M, 
double Rmin, 
const Vector2D& center):
     5   M_(M),Rmin_(Rmin),center_(center){}
     9  const vector<ComputationalCell>& ,
    10  const vector<Extensive>& ,
    16   const double r = 
abs(pos);
    17   return (-1)*pos*M_/(r*r*r+Rmin_*Rmin_*Rmin_);
 Abstract class for tessellation. 
virtual Vector2D const  & GetCellCM(int index) const =0
Returns Position of Cell's CM. 
Point source gravity force. 
Class for keeping the names of the tracers and stickers. 
CenterGravity(double M, double Rmin, const Vector2D ¢er)
Class constructor. 
double abs(Vector3D const &v)
Norm of a vector.