code: def test_armodel():
      for i in range(1, 4):
          model = regression.ARModel(x, i)
          for i in range(20):
              results = model.fit(y)
              rho, sigma = regression.yule_walker(y - results.predicted)
              model = regression.ARModel(model.design, rho)
          print("AR coefficients:", model.rho)
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_armodel() without return types