Clustering coefficient of a country is the probability of trade relationships exist between the partners of
this country. It reflects the closeness of the neighbors. If a country’s neighbor in the network is closely
related, the country owns a higher clustering coefficient; on the contrary, if a country’s neighbor is loosely
related, the clustering coefficient of this country is lower. The weighted clustering coefficient takes into
account not only the gathering of the network, but also considers the weights of the edges.