(The change point of mean is a commonly used change point analysis method in statistics. Its main ideas are as follows: If there is a set of data, as a certain index changes (enlargement), its value increases gradually and tends to be stable. How to judge whether there is a sudden change in the process and the unusual situation? The mean change point analysis method provides a way of thinking, which is as follows: 1 the total mean and variance are calculated. The 2 cycle divides the ordered data into two groups, X1, X2. Calculate the mean and variance of each group. The difference between the sum of the total variance and the group variance is calculated. 3 get a change point)