中文说明：此代码用于使用MM1模型对队列进行建模；包含一个队列和一个服务器，到达间隔是指数随机数，服务时间也是指数的。结果显示系统的利用率和吞吐量；
English Description：
this code is used to model queue using MM1 model ; contains one queue and one server, the inter-arrival is exponential random number, the service time is also exponential. the result show the utilization and throughput of the system