code: def breaks_hansen(olsresults):
      """
      Test for model stability, breaks in parameters for ols, Hansen 1992
  
      Parameters
      ----------
      olsresults : RegressionResults
          Results from estimation of a regression model.
  
      Returns
      -------
      teststat : float
          Hansen's test statistic.
      crit : ndarray
          The critical values at alpha=0.95 for different nvars.
  
      Notes
      -----
      looks good in example, maybe not very powerful for small changes in
      parameters
  
      According to Greene, distribution of test statistics depends on nvar but
      not on nobs.
  
      Test statistic is verified against R:strucchange
  
      References
      ----------
      Greene section 7.5.1, notation follows Greene
      """
      x = olsresults.model.exog
      resid = array_like(
          olsresults.resid, "resid", shape=(x.shape[0], 1)
      )
      nobs, nvars = x.shape
      resid2 = resid**2
      ft = np.c_[x * resid[:, None], (resid2 - resid2.mean())]
      score = ft.cumsum(0)
      f = nobs * (ft[:, :, None] * ft[:, None, :]).sum(0)
      s = (score[:, :, None] * score[:, None, :]).sum(0)
      h = np.trace(np.dot(np.linalg.inv(f), s))
      crit95 = np.array(
          [(2, 1.01), (6, 1.9), (15, 3.75), (19, 4.52)],
          dtype=[("nobs", int), ("crit", float)],
      )
      # TODO: get critical values from Bruce Hansen's 1992 paper
      return h, crit95
  
imports: from statsmodels.compat.pandas import deprecate_kwarg
  from collections.abc import Iterable
  import numpy
  import pandas
  from scipy import stats
  from statsmodels.regression.linear_model import OLS, RegressionResultsWrapper
  from statsmodels.stats._adnorm import anderson_statistic, normal_ad
  from statsmodels.stats._lilliefors import kstest_exponential, kstest_fit, kstest_normal, lilliefors
  from statsmodels.tools.validation import array_like, bool_like, dict_like, float_like, int_like, string_like
  from statsmodels.tsa.tsatools import lagmat
label_desc: Use image node_id 20 for calling a global function with example usage: breaks_hansen(olsresults) and returns: h,  crit95