'Indicated if an observation takes the same value as the next
ordered observation.
Parameters
endog: array
Models endogenous variable
censors: array
arrat indicating a censored array
Returns
indic_ties: array
ties[i]=1 if endog[i]==endog[i+1] and
censors[i]=censors[i+1]'

def _is_tied(self, endog, censors):

    nobs = int(self.nobs)
    endog_idx = (endog[np.arange((nobs - 1))] == endog[(np.arange((nobs - 1)) + 1)])
    censors_idx = (censors[np.arange((nobs - 1))] == censors[(np.arange((nobs - 1)) + 1)])
    indic_ties = (endog_idx * censors_idx)
    return np.int_(indic_ties)
