code: def prior_const(C, alpha=0.001):
      
      B = alpha * np.ones(C.shape)
      return B
docs: Constant prior of strength alpha.
  
      Prior is defined via
  
          b_ij=alpha for all i,j
  
      Parameters
      ----------
      C : (M, M) ndarray or scipy.sparse matrix
          Count matrix
      alpha : float (optional)
          Value of prior counts
  
      Returns
      -------
      B : (M, M) ndarray
          Prior count matrix