说明：  计算Diebold and Yilmaz(2014)溢出指数 Diebold F X, Yilmaz K. Better to give than to receive: Predictive directional measurement of volatility spillovers. International Journal of Forecasting, 2012, 28(1): 57-66.
(Diebold and Yilmaz(2014) spillover index Diebold F X, Yilmaz K. Better to give than to receive: Predictive directional measurement of volatility spillovers. International Journal of Forecasting, 2012, 28(1): 57-66.)