Instantiate a random variable and apply annual growth factors.

        :return:

def generate_values(self, *args, **kwargs):
        """
        Instantiate a random variable and apply annual growth factors.

        :return:
        """
        values = super().generate_values(*args, **kwargs, size=(len(self.times) * self.size,))
        alpha = self.cagr

        # @todo - fill to cover the entire time: define rules for filling first
        ref_date = self.ref_date if self.ref_date else self.times[0].to_pydatetime()
        # assert ref_date >= self.times[0].to_pydatetime(), 'Ref date must be within variable time span.'
        # assert ref_date <= self.times[-1].to_pydatetime(), 'Ref date must be within variable time span.'

        start_date = self.times[0].to_pydatetime()
        end_date = self.times[-1].to_pydatetime()

        a = growth_coefficients(start_date, end_date, ref_date, alpha, self.size)

        values *= a.ravel()

        df = pd.DataFrame(values)
        df.columns = [kwargs['name']]
        df.set_index(self._multi_index, inplace=True)
        # @todo this is a hack to return a series with index as I don't know how to set an index and rename a series
        data_series = df.iloc[:, 0]
        data_series._metadata = kwargs
        data_series.index.rename(['time', 'samples'], inplace=True)

        return data_series