3822.sagews

data = [
  [0, 1],
  [1, 2],
  [2, 1],
  [3, 3.5],
  [4, 5.5]
]
model = PolynomialRing(RR, x).lagrange_polynomial(data)(x)
scatter_plot(data) + plot(model, (x, 0, 4))