说明：  用蒙特卡洛求圆周率，人为的构造一个合适的概率模型，依照对该模型进行大量的统计实验，使它的统计参量正好是待求问题的解。
(Monte Carlo is used to calculate the PI, and a suitable probability model is constructed artificially. According to a large number of statistical experiments on the model, its statistical parameters are just the solution of the problem to be solved.)