template <int dim>
class FDVec {
 private:
  double e[dim];
 public:
  FDVec()
  {
    for ( int i = 0; i < dim; i++ )   e[i] = 0.0;
  }

  // Member function: x.sum(y,out): returns out <- x + y
  FDVec<dim> &sum(const FDVec<dim> &y, FDVec<dim> &out)
  {
    for ( int i = 0; i < dim; i++ )
      out.e[i] = e[i] + y.e[i];
    return out;
  }
  

  // Member function: x.mult(s,out): returns out <- s*x
  FDVec<dim> &mult(double s, FDVec<dim> &out)
  {
    for ( int i = 0; i < dim; i++ )
      out.e[i] = s*e[i];
  }
  
};