class_docstr: Provides optimization functions used in estimating and conducting
  inference in an AFT model.
  
  Methods
  ------
  
  _opt_wtd_nuis_regress:
      Function optimized over nuisance parameters to compute
      the profile likelihood
  
  _EM_test:
      Uses the modified Em algorithm of Zhou 2005 to maximize the
      likelihood of a parameter vector.
class_docstr_tok: ["Provides","optimization","functions","used","in","estimating","and","conducting","inference","in","an","AFT","model",".","Methods","--","--","--","_opt_wtd_nuis_regress",":","Function","optimized","over","nuisance","parameters","to","compute","the","profile","likelihood","_EM_test",":","Uses","the","modified","Em","algorithm","of","Zhou","2005","to","maximize","the","likelihood","of","a","parameter","vector","."]
docstr: Returns the difference between the log likelihood for a
  parameter and some critical value.
  
  Parameters
  ----------
  b0: float
      Value of a regression parameter
  param_num : int
      Parameter index of b0
docstr_tok: ["Returns","the","difference","between","the","log","likelihood","for","a","parameter","and","some","critical","value",".","Parameters","--","--","--","--","--","b0",":","float","Value","of","a","regression","parameter","param_num",":","int","Parameter","index","of","b0"]
code: def _ci_limits_beta(self, b0, param_num=None):
      """
      Returns the difference between the log likelihood for a
      parameter and some critical value.
  
      Parameters
      ----------
      b0: float
          Value of a regression parameter
      param_num : int
          Parameter index of b0
      """
      return self.test_beta([b0], [param_num])[0] - self.r0
  
imports: import warnings
  import numpy
  from scipy import optimize
  from scipy.stats import chi2
  from statsmodels.regression.linear_model import OLS, WLS
  from statsmodels.tools import add_constant
  from statsmodels.tools.sm_exceptions import IterationLimitWarning
  from .descriptive import _OptFuncts
label_desc: Use image node_id 4 for calling the OptAFT obj's underlying member method code with example usage: obj._ci_limits_beta(b0, param_num) and returns: unknown