说明：  这个函数，很重要，不是用不行，这是一个泊松分布，是一个一维的，长度是1000的分布，还可以自己添加plot绘图函数，查看泊松分布。
(This function is very important, do not use this function, very important, not with no, this is a poisson distribution is a one-dimensional, length is 1000 distribution, still can add your own plot drawing function, check poisson distribution. No, use your Linux will be very smooth.)