说明：  通过寻找一组在状态空间中传播的随机样本来近似的表示概率密度函数，用样本均值代替积分运算，进而获得系统状态的最小方差估计的过程
(By finding a set of random samples propagating in the state space to approximate the probability density function, the sample mean is used instead of the integral operation to obtain the minimum variance estimation of the system state)