docs: protected void addToStatistics(NumberVector nv) {
      final int d = nv.getDimensionality();
      assert (d == ls.length);
      this.n++;
      for(int i = 0; i < d; i++) {
        double v = nv.doubleValue(i);
        ls[i] += v;
        ss += v * v;
      }
    }