struct p {
  Float operator() (const point& x) const {
    if (d == 2) return 26*(pow(x[0],5) - 10*pow(x[0],3)*sqr(x[1]) 
                                       + 5*x[0]*pow(x[1],4));
    else        return 3*sqr(x[0])*x[1] - pow(x[1],3);
  }
  p (size_t d1) : d(d1) {}
  protected: size_t d;
};
struct f {
  Float operator() (const point& x) const {
    if (d == 2) return _p(x)/pow(norm(x),5);
    else        return alpha*_p(x);
  }
  f (size_t d1) : d(d1), _p(d1) {
    Float pi = acos(Float(-1));
    alpha = -(13./8.)*sqrt(35./pi);
  }
  protected: size_t d; p _p; Float alpha;
};
struct u_exact {
  Float operator() (const point& x) const {
    if (d == 2) return _f(x)/(25+sqr(norm(x)));
    else        return sqr(norm(x))/(12+sqr(norm(x)))*_f(x);
  }
  u_exact (size_t d1) : d(d1), _f(d1) {}
  protected: size_t d; f _f;
};
Float phi (const point& x) { return norm(x) - 1; }
