// Specializations of FCVec template for 2-dim'l vectors
template<> 
class FDVec<2> {
  private:
   double e[2];
  public:
  FDVec() { e[0] = e[1] = 0.0; }
  FDVec<2> &sum(FDVec<2> &y, FDVec<2> &out)
  { 
    out.e[0] = e[0] + y.e[0];  out.e[1] = e[1] + y.e[1]; 
    return out;
  }
  FDVec<2> &mult(double s, FDVec<2> &out)
  { 
    out.e[0] = s*e[0];  out.e[1] = s*e[1]; 
    return out; 
  }
}