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 __init__(self, endog, **kwargs):
      k_states = 1
      k_posdef = 2
      super().__init__(
          endog, k_states=k_states, k_posdef=k_posdef, **kwargs
      )
      self["design", 0, 0] = 1
      self["selection", 0, 0] = 1
      self["state_cov", 1, 1] = 1
      self.initialize_stationary()
  
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 1 to create a new LargeStateCovAR1 object from inherited base classes: mlemodel with example: obj = LargeStateCovAR1(endog)