'Initializes the model for the IRLS fit.
Resets the history and number of iterations.'

def _initialize(self):

    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 = np.float((self.exog.shape[0] - np_matrix_rank(self.exog)))
    self.df_model = np.float((np_matrix_rank(self.exog) - 1))
    self.nobs = float(self.endog.shape[0])
