code: def count_matrix(self):
          # TODO: does this belong here or to the BHMM sampler, or in a subclass containing HMM with data?
          
          if self.hidden_state_trajectories is None:
              raise RuntimeError('HMM model does not have a hidden state trajectory.')
  
          C = msmest.count_matrix(self.hidden_state_trajectories, 1, nstates=self._nstates)
          return C.toarray()
docs: Compute the transition count matrix from hidden state trajectory.
  
          Returns
          -------
          C : numpy.array with shape (nstates,nstates)
              C[i,j] is the number of transitions observed from state i to state j
  
          Raises
          ------
          RuntimeError
              A RuntimeError is raised if the HMM model does not yet have a hidden state trajectory associated with it.
  
          Examples
          --------