def ttest_interaction(self):
        '''ttests for no-interaction terms are zero
        '''
        #use self.r_nointer instead
        nia = self.n_interaction
        R_nointer = np.hstack((np.zeros((nia, nia-self.nvars)), np.eye(nia)))
        #inter_direct = resols_full_dropf.tval[-nia:]
        R_nointer_transf = self.transform.inv_dot_right(R_nointer)
        self.R_nointer_transf = R_nointer_transf
        t_res = self.resols.t_test(R_nointer_transf)
        return t_res
dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/sandbox/stats/contrast_tools.py/TwoWay.ttest_interaction/swapped operands of `-`