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