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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def plot_knee(self, ):
 """ Plot the curve and the knee, if it exists """

        import matplotlib.pyplot as plt

        plt.figure(figsize=(8, 8))
        plt.plot(self.x, self.y)
        plt.vlines(self.knee, plt.ylim()[0], plt.ylim()[1])