def correlation(s, o):
    """
        correlation coefficient
        input:
        s: simulated
        o: observed
        output:
        correlation: correlation coefficient
        """
    # s,o = filter_nan(s,o)
    if s.size == 0:
        corr = np.NaN
    else:
        corr = np.corrcoef(o, s)[0, 1]
    return corr
correlation coefficient
        input:
        s: simulated
        o: observed
        output:
        correlation: correlation coefficient