- unsigned n = loads.size();
- load_avg = std::accumulate(loads.begin(), loads.end(), 0.0) / n;
- double variance = 0.0;
- double epsilon = 0.0;
- for (unsigned i = 0 ; i < n ; ++i) {
- double diff = loads[i] - load_avg;
- variance += diff * diff;
- epsilon += diff;
+ using std::tr1::bind;
+ using std::tr1::placeholders::_1;
+
+ unsigned n = vec.size();
+ double vec_sum = std::accumulate(vec.begin(), vec.end(), 0.0);
+ double vec_avg = vec_sum / n;
+
+ if (sum)
+ *sum = vec_sum;
+ if (avg)
+ *avg = vec_avg;
+
+ if (stddev) {
+ std::vector<double> diff(vec);
+ std::transform(diff.begin(), diff.end(), diff.begin(),
+ bind(std::minus<double>(), _1, vec_avg));
+ double epsilon = std::accumulate(diff.begin(), diff.end(), 0.0);
+ double square_sum = std::inner_product(diff.begin(), diff.end(),
+ diff.begin(), 0.0);
+ double variance = (square_sum - (epsilon * epsilon) / n) / n;
+ *stddev = sqrt(variance);