code: def is_rate_matrix(K, tol=1e-10):
      
      R = K - K.diagonal()
      off_diagonal_positive = np.allclose(R, abs(R), 0.0, atol=tol)
  
      row_sum = K.sum(axis=1)
      row_sum_eq_0 = np.allclose(row_sum, 0.0, atol=tol)
  
      return off_diagonal_positive and row_sum_eq_0
docs: True if K is a rate matrix
      Parameters
      ----------
      K : numpy.ndarray matrix
          Matrix to check
      tol : float
          tolerance to check with
  
      Returns
      -------
      Truth value : bool
          True, if K negated diagonal is positive and row sums up to zero.
          False, otherwise