code: def posterior_sum(self):
      return self.nphi.sum(1) + self.prior * self.nphi.shape[1]
  
imports: import collections
  import functools
  import io
  import os
  import warnings
  import dgl
  import numpy
  import scipy
  import torch
label_desc: Use image node_id 3 for calling the _Dirichlet obj's underlying member method code with example usage: obj.posterior_sum() and returns: unknown