code: def subtract(self, other):
          
          self_estimate = getattr(self, self._estimate_name)
          other_estimate = getattr(other, other._estimate_name)
          new_index = np.concatenate((other_estimate.index, self_estimate.index))
          new_index = np.unique(new_index)
          return pd.DataFrame(
              self_estimate.reindex(new_index, method="ffill").values
              - other_estimate.reindex(new_index, method="ffill").values,
              index=new_index,
              columns=["diff"],
          )
docs: Subtract the {0} of two {1} objects.
  
          Parameters
          ----------
          other: an {1} fitted instance.