def add_empty_dataset(self, value=1):
        """Create an empty data set. Empty means: all elements have the same
        value.

        Parameters
        ----------
        value: float, optional
            which value to assign all element parameters. Default is one.
        """
        subdata = np.ones(self.grid.nr_of_elements) * value
        pid = self.add_data(subdata)
        return pid