반환값
        -------
        self : LogisticRegressionGD 객체

        """
        rgen = np.random.RandomState(self.random_state)
        self.w_ = rgen.normal(loc=0.0, scale=0.01, size=X.shape[1])
        self.b_ = np.float_(0.)
        self.losses_ = []
        for i in range(self.n_iter):
            net_input = self.net_input(X)
            output = self.activation(net_input)
            errors = (y - output)
            self.w_ += self.eta * 2.0 * X.T.dot(errors) / X.shape[0]
            self.b_ += self.eta * 2.0 * errors.mean()
            loss = (-y.dot(np.log(output))
                   - ((1 - y).dot(np.log(1 - output)))
                    / X.shape[0])
            self.losses_.append(loss)
        return self
    
    def net_input(self, X):
        """최종 입력 계산"""
        return np.dot(X, self.w_) + self.b_