def DG2017_predict(dictio, a=0.096, b=0.663):
    """Calculate the K coefficient for the DG2017 method.

    Parameters
    ----------
    dictio: dict
        a dictionary with ndarrays named "feo" and "rws"
    a and b: float
        factors in the equation: K = a * [FeO wt%] + b; default values from Di Genova et al. (2017)

    Returns
    -------
    H2O (wt %): ndarray
        The water content of the glasses calculated as Rws * (a * [FeO wt%] + b)

    """
    return dictio['rws'] * (dictio['feo'] * a + b)
