code: private static double dotProduct(DoubleVector u,
                                       DoubleVector v) {
          double dot = 0;
          for (int i = 0; i < u.length(); ++i) {
              double a = u.get(i);
              double b = v.get(i);
              dot += u.get(i) * v.get(i);
          }
          return dot;
      }
docs: Compute the dot product between two vectors.