docstr: Initializes the model for the IRLS fit.
  
  Resets the history and number of iterations.
code: def _initialize(self):
      """
      Initializes the model for the IRLS fit.
  
      Resets the history and number of iterations.
      """
      self.pinv_wexog = np.linalg.pinv(self.exog)
      self.normalized_cov_params = np.dot(
          self.pinv_wexog, np.transpose(self.pinv_wexog)
      )
      self.df_resid = float(
          self.exog.shape[0] - np.linalg.matrix_rank(self.exog)
      )
      self.df_model = float(np.linalg.matrix_rank(self.exog) - 1)
      self.nobs = float(self.endog.shape[0])
  
imports: import numpy
  import scipy.stats
  import statsmodels.base.model
  import statsmodels.base.wrapper
  import statsmodels.regression._tools
  import statsmodels.regression.linear_model
  import statsmodels.robust.norms
  import statsmodels.robust.scale
  from statsmodels.tools.decorators import cache_readonly
  from statsmodels.tools.sm_exceptions import ConvergenceWarning
label_desc: Use image node_id 2 for calling the RLM obj's underlying member method code with example usage: obj._initialize() without return types