Calculate mean and standard error of the mean.

mean_and_sem.cc

template <typename T>
std::pair<T, T> MeanAndError(const std::vector<T> &v) {
  using namespace std;
  T mean = accumulate(begin(v), end(v), T(0)) / v.size();
  vector<T> diff(v.size());
  transform(begin(v), end(v), begin(diff), std::bind2nd(minus<T>(), mean));
  T sq_sum = inner_product(begin(diff), end(diff), begin(diff), T(0));
  T sem = sqrt(sq_sum / (v.size() * (v.size() - 1)));
  return make_pair(mean, sem);
}