class_docstr: Test class for k_posdef > k_states (which usually do not get tested in
  other models).
  
  This is just an AR(1) model with an extra unused state innovation
code: def update(self, params, **kwargs):
      params = super().update(params, **kwargs)
  
      self["transition", 0, 0] = params[0]
      self["state_cov", 0, 0] = params[1]
  
imports: import numpy
  import pandas
  import os
  import pytest
  from statsmodels.tsa.statespace import mlemodel, sarimax
  from statsmodels import datasets
  from numpy.testing import assert_equal, assert_allclose, assert_raises
label_desc: Use image node_id 4 for calling the LargeStateCovAR1 obj's underlying member method code with example usage: obj.update(params) without return types