def coupl_model1(self):
        """ In model 1, we want enforce the following signs
            on the couplings. Model 2 has the same couplings
            but arbitrary signs.
        """
        self.Coupl[0,0] = np.abs(self.Coupl[0,0])
        self.Coupl[0,1] = -np.abs(self.Coupl[0,1])
        self.Coupl[1,1] = np.abs(self.Coupl[1,1])