def aic(llf, nobs, df_modelwc):
    """
    Akaike information criterion

    Parameters
    ----------
    llf : {float, array_like}
        value of the loglikelihood
    nobs : int
        number of observations
    df_modelwc : int
        number of parameters including constant

    Returns
    -------
    aic : float
        information criterion

    References
    ----------
    https://en.wikipedia.org/wiki/Akaike_information_criterion
    """
    return -2.0 * llf + 2.0 * df_modelwc