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 start_params(self):
      return [0.5, 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 3 for calling the LargeStateCovAR1 obj's underlying member method code with example usage: obj.start_params() and returns: list