////////////////////////////////////////////////////////////////////////////////
template <typename T> struct zero;
template <> struct zero<short> {
  constexpr short operator()() const { return 0; }
};
template <> struct zero<int> {
  constexpr int operator()() const { return 0; }
};
template <> struct zero<long> {
  constexpr long operator()() const { return 0; }
};
template <> struct zero<float> {
  constexpr float operator()() const { return 0; }
};
template <> struct zero<double> {
  constexpr double operator()() const { return 0; }
};

template <typename T, int D> struct zero<vect<T, D> > {
  constexpr vect<T, D> operator()() { return vect<T, D>(); }
};