def index_agreement(s, o):
    """
        index of agreement
        input:
        s: simulated
        o: observed
        output:
        ia: index of agreement
        """
    # s,o = filter_nan(s,o)
    ia = 1 - (np.sum((o-s)**2)) /\
             (np.sum((np.abs(s-np.mean(o))+np.abs(o-np.mean(o)))**2))
    return ia
index of agreement
        input:
        s: simulated
        o: observed
        output:
        ia: index of agreement