computes the empirical correlation coefficient

def corr(label, pred):
    """computes the empirical correlation coefficient"""
    numerator1 = label - np.mean(label, axis=0)
    numerator2 = pred - np.mean(pred, axis = 0)
    numerator = np.mean(numerator1 * numerator2, axis=0)
    denominator = np.std(label, axis=0) * np.std(pred, axis=0)
    return np.mean(numerator / denominator)