code: def internal_tally(self):
          
          chain = []
          for stochastic in self.stochastics:
              chain.append(np.ravel(stochastic.value))
          self._trace.append(np.concatenate(chain))
docs: Store the trace of stochastics for the computation of the covariance.
          This trace is completely independent from the backend used by the
          sampler to store the samples.