code: def reset_parcov(self,arg=None):
          
          self.logger.statement("resetting parcov")
          self.__parcov = None
          if arg is not None:
              self.parcov_arg = arg
docs: reset the parcov attribute to None
  
          Parameters
          ----------
          arg : str or pyemu.Matrix
              the value to assign to the parcov attribute.  If None,
              the private __parcov attribute is cleared but not reset