code: def C(w, Xs):
      '''Calculate the cylinder center given the cylinder direction and 
      a list of data points.
      '''
      n = len(Xs)
      P = projection_matrix(w)
      Ys = [np.dot(P, X) for X in Xs]
      A = calc_A(Ys)
      A_hat = calc_A_hat(A, skew_matrix(w))
  
      return np.dot(A_hat, sum(np.dot(Y, Y) * Y for Y in Ys)) / np.trace(np.dot(A_hat, A)f C(w, Xs):
      '''Calculate the cylinder center given the cylinder direction and 
      a list of data points.
      '''
      n = len(Xs)
      P = projection_matrix(w)
      Ys = [np.dot(P, X) for X in Xs]
      A = calc_A(Ys)
      A_hat = calc_A_hat(A, skew_matrix(w))
  
      return np.dot(A_hat, sum(np.dot(Y, Y) * Y for Y in Ys)) / np.trace(np.dot(A_hat, A))
docs: Calculate the cylinder center given the cylinder direction and 
      a list of data points.