docs: public double[][] getR() {
      double[][] R = new double[n][n];
      for(int i = 0; i < n; i++) {
        System.arraycopy(QR[i], i + 1, R[i], i + 1, n - i - 1);
        R[i][i] = Rdiag[i];
      }
      return R;
    }