code: def coupl_model1(self):
          
          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])
docs: In model 1, we want enforce the following signs
              on the couplings. Model 2 has the same couplings
              but arbitrary signs.