code: def r(w, Xs):
      '''Calculate the radius given the cylinder direction and a list
      of data points.
      '''
      n = len(Xs)
      P = projection_matrix(w)
      c = C(w, Xs)
  
      return np.sqrt(sum(np.dot(c - X, np.dot(P, c - X)) for X in Xs) / nf r(w, Xs):
      '''Calculate the radius given the cylinder direction and a list
      of data points.
      '''
      n = len(Xs)
      P = projection_matrix(w)
      c = C(w, Xs)
  
      return np.sqrt(sum(np.dot(c - X, np.dot(P, c - X)) for X in Xs) / n)
docs: Calculate the radius given the cylinder direction and a list
      of data points.