code: def copy_data_ext(self, model, field, dest=None, idx=None, astype=None):
          
          # use default destination
  
          if not dest:
              dest = field
          assert dest not in self._states + self._algebs
  
          self.__dict__[dest] = self.read_data_ext(
              model, field, idx, astype=astype)
  
          if idx is not None:
              if len(idx) == self.n:
                  self.link_to(model, idx, self.idx)
docs: Retrieve the field of another model and store it as a field.
  
          :param model: name of the source model being a model name or a group name
          :param field: name of the field to retrieve
          :param dest: name of the destination field in ``self``
          :param idx: idx of elements to access
          :param astype: type cast
  
          :type model: str
          :type field: str
          :type dest: str
          :type idx: list, matrix
          :type astype: None, list, matrix
  
          :return: None