Plots the normalized curve, the distance curve (xd, ysn) and the
        knee, if it exists.

def plot_knee_normalized(self, ):
        """
        Plots the normalized curve, the distance curve (xd, ysn) and the
        knee, if it exists.

        """
        import matplotlib.pyplot as plt

        plt.figure(figsize=(8, 8))
        plt.plot(self.xsn, self.ysn)
        plt.plot(self.xd, self.yd, 'r')
        plt.xticks(np.arange(min(self.xsn), max(self.xsn) + 0.1, 0.1))
        plt.yticks(np.arange(min(self.xd), max(self.ysn) + 0.1, 0.1))

        plt.vlines(self.norm_knee, plt.ylim()[0], plt.ylim()[1])