Seebeck analytic formula in the single parabolic model

def seebeck_spb(eta,Lambda=0.5):
    """
        Seebeck analytic formula in the single parabolic model
    """
    from fdint import fdk
    
    return constants.k/constants.e * ((2. + Lambda) * fdk( 1.+ Lambda, eta)/ 
                 ((1.+Lambda)*fdk(Lambda, eta))- eta) * 1e+6