def max_dropback(self):
        """最大回撤
        """
        return round(
            float(
                max(
                    [
                        (self.assets.iloc[idx] - self.assets.iloc[idx::].min())
                        / self.assets.iloc[idx]
                        for idx in range(len(self.assets))
                    ]
                )
            ),
            2
        )