code: public double[][] getH() {
      double[][] H = new double[m][n];
      for(int i = 0; i < m; i++) {
        System.arraycopy(QR[i], 0, H[i], 0, i < n ? i : n);
      }
      return H;
    }
docs: Return the Householder vectors
  
  @return Lower trapezoidal matrix whose columns define the reflections