def NRTL(xs, taus, alphas):
gammas = []<EOL>cmps = range(len(xs))<EOL>Gs = [[exp(-alphas[i][j]*taus[i][j]) for j in cmps] for i in cmps]<EOL>for i in cmps:<EOL><INDENT>tn1, td1, total2 = <NUM_LIT:0.>, <NUM_LIT:0.>, <NUM_LIT:0.><EOL>for j in cmps:<EOL><INDENT>tn1 += xs[j]*taus[j][i]*Gs[j][i]<EOL>td1 +=  xs[j]*Gs[j][i]<EOL>tn2 = xs[j]*Gs[i][j]<EOL>td2 = td3 = sum([xs[k]*Gs[k][j] for k in cmps])<EOL>tn3 = sum([xs[m]*taus[m][j]*Gs[m][j] for m in cmps])<EOL>total2 += tn2/td2*(taus[i][j] - tn3/td3)<EOL><DEDENT>gamma = exp(tn1/td1 + total2)<EOL>gammas.append(gamma)<EOL><DEDENT>return gammas<EOL>
r'''Calculates the activity coefficients of each species in a mixture
    using the Non-Random Two-Liquid (NRTL) method, given their mole fractions,
    dimensionless interaction parameters, and nonrandomness constants. Those
    are normally correlated with temperature in some form, and need to be
    calculated separately.

    .. math::
        \ln(\gamma_i)=\frac{\displaystyle\sum_{j=1}^{n}{x_{j}\tau_{ji}G_{ji}}}
        {\displaystyle\sum_{k=1}^{n}{x_{k}G_{ki}}}+\sum_{j=1}^{n}
        {\frac{x_{j}G_{ij}}{\displaystyle\sum_{k=1}^{n}{x_{k}G_{kj}}}}
        {\left ({\tau_{ij}-\frac{\displaystyle\sum_{m=1}^{n}{x_{m}\tau_{mj}
        G_{mj}}}{\displaystyle\sum_{k=1}^{n}{x_{k}G_{kj}}}}\right )}

        G_{ij}=\text{exp}\left ({-\alpha_{ij}\tau_{ij}}\right )

    Parameters
    ----------
    xs : list[float]
        Liquid mole fractions of each species, [-]
    taus : list[list[float]]
        Dimensionless interaction parameters of each compound with each other,
        [-]
    alphas : list[list[float]]
        Nonrandomness constants of each compound interacting with each other, [-]

    Returns
    -------
    gammas : list[float]
        Activity coefficient for each species in the liquid mixture, [-]

    Notes
    -----
    This model needs N^2 parameters.

    One common temperature dependence of the nonrandomness constants is:

    .. math::
        \alpha_{ij}=c_{ij}+d_{ij}T

    Most correlations for the interaction parameters include some of the terms
    shown in the following form:

    .. math::
        \tau_{ij}=A_{ij}+\frac{B_{ij}}{T}+\frac{C_{ij}}{T^{2}}+D_{ij}
        \ln{\left ({T}\right )}+E_{ij}T^{F_{ij}}

    Examples
    --------
    Ethanol-water example, at 343.15 K and 1 MPa:

    >>> NRTL(xs=[0.252, 0.748], taus=[[0, -0.178], [1.963, 0]],
    ... alphas=[[0, 0.2974],[.2974, 0]])
    [1.9363183763514304, 1.1537609663170014]

    References
    ----------
    .. [1] Renon, Henri, and J. M. Prausnitz. "Local Compositions in
       Thermodynamic Excess Functions for Liquid Mixtures." AIChE Journal 14,
       no. 1 (1968): 135-144. doi:10.1002/aic.690140124.
    .. [2] Gmehling, Jurgen, Barbel Kolbe, Michael Kleiber, and Jurgen Rarey.
       Chemical Thermodynamics for Process Simulation. 1st edition. Weinheim:
       Wiley-VCH, 2012.