Minimise volatility.

        :return: asset weights for the volatility-minimising portfolio
        :rtype: dict

def min_volatility(self):
        """
        Minimise volatility.

        :return: asset weights for the volatility-minimising portfolio
        :rtype: dict
        """
        args = (self.cov_matrix, self.gamma)
        result = sco.minimize(
            objective_functions.volatility,
            x0=self.initial_guess,
            args=args,
            method="SLSQP",
            bounds=self.bounds,
            constraints=self.constraints,
        )
        self.weights = result["x"]
        return dict(zip(self.tickers, self.weights))