code: def hilbert_array(xint):
      
      N, d = xint.shape
      h = np.zeros(N, int64)
      for n in range(N):
          h[n] = Hilbert_to_int(xint[n, :])
      return h
docs: Compute Hilbert indices. 
  
      Parameters
      ----------
      xint: (N, d) int numpy.ndarray
  
      Returns
      -------
      h: (N,) int numpy.ndarray
          Hilbert indices