说明：  Copula函数描述的是变量间的相关性，实际上是一类将联合分布函数与它们各自的边缘分布函数连接在一起的函数，因此也有人将它称为连接函数。本程序已调试，可以运行。
(Copula function describes the correlation between variables, in fact, is a class of joint distribution functions and their respective edge distribution functions connected together, so it is also called the connection function. This procedure has been debugging, you can run.)