📝 add anomaly detection readme

Author: lawlite19

readme.md

@@ -1032,19 +1032,24 @@ from sklearn.preprocessing import StandardScaler
 ## 七、异常检测 Anomaly Detection
 - [全部代码](/AnomalyDetection/AnomalyDetection.py)
 
-### 1、异常检测流程
-- ![$${x^{(i)}}$$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24%7Bx%5E%7B%28i%29%7D%7D%24%24)对应feature
-- 建立模型model：`P(x)`
-- 检查若是：`P(x)<ε`，则认为是异常,其中`ε`为我们要求的概率的临界值`threshold`
-
-### 2、高斯分布（正态分布）`Gaussian distribution` 
+### 1、高斯分布（正态分布）`Gaussian distribution` 
 - 分布函数：![$$p(x) = {1 \over {\sqrt {2\pi } \sigma }}{e^{ - {{{{(x - u)}^2}} \over {2{\sigma ^2}}}}}$$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24p%28x%29%20%3D%20%7B1%20%5Cover%20%7B%5Csqrt%20%7B2%5Cpi%20%7D%20%5Csigma%20%7D%7D%7Be%5E%7B%20-%20%7B%7B%7B%7B%28x%20-%20u%29%7D%5E2%7D%7D%20%5Cover%20%7B2%7B%5Csigma%20%5E2%7D%7D%7D%7D%7D%24%24)
  - 其中，`u`为数据的**均值**，`σ`为数据的**标准差**
  - `σ`越**小**，对应的图像越**尖**
 - 参数估计（`parameter estimation`）
  - ![$$u = {1 \over m}\sum\limits_{i = 1}^m {{x^{(i)}}} $$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24u%20%3D%20%7B1%20%5Cover%20m%7D%5Csum%5Climits_%7Bi%20%3D%201%7D%5Em%20%7B%7Bx%5E%7B%28i%29%7D%7D%7D%20%24%24)
  - ![$${\sigma ^2} = {1 \over m}\sum\limits_{i = 1}^m {{{({x^{(i)}} - u)}^2}} $$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24%7B%5Csigma%20%5E2%7D%20%3D%20%7B1%20%5Cover%20m%7D%5Csum%5Climits_%7Bi%20%3D%201%7D%5Em%20%7B%7B%7B%28%7Bx%5E%7B%28i%29%7D%7D%20-%20u%29%7D%5E2%7D%7D%20%24%24)
 
+### 2、异常检测算法
+- 例子
+ - 训练集：![$$\{ {x^{(1)}},{x^{(2)}}, \cdots {x^{(m)}}\} $$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24%5C%7B%20%7Bx%5E%7B%281%29%7D%7D%2C%7Bx%5E%7B%282%29%7D%7D%2C%20%5Ccdots%20%7Bx%5E%7B%28m%29%7D%7D%5C%7D%20%24%24),其中![$$x \in {R^n}$$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24x%20%5Cin%20%7BR%5En%7D%24%24)
+ - 假设![$${x_1},{x_2} \cdots {x_n}$$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24%7Bx_1%7D%2C%7Bx_2%7D%20%5Ccdots%20%7Bx_n%7D%24%24)相互独立，建立model模型：![$$p(x) = p({x_1};{u_1},\sigma _1^2)p({x_2};{u_2},\sigma _2^2) \cdots p({x_n};{u_n},\sigma _n^2) = \prod\limits_{j = 1}^n {p({x_j};{u_j},\sigma _j^2)} $$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24p%28x%29%20%3D%20p%28%7Bx_1%7D%3B%7Bu_1%7D%2C%5Csigma%20_1%5E2%29p%28%7Bx_2%7D%3B%7Bu_2%7D%2C%5Csigma%20_2%5E2%29%20%5Ccdots%20p%28%7Bx_n%7D%3B%7Bu_n%7D%2C%5Csigma%20_n%5E2%29%20%3D%20%5Cprod%5Climits_%7Bj%20%3D%201%7D%5En%20%7Bp%28%7Bx_j%7D%3B%7Bu_j%7D%2C%5Csigma%20_j%5E2%29%7D%20%24%24)
+- 过程
+ - 选择具有代表异常的`feature`:xi
+ - 参数估计：![$${u_1},{u_2}, \cdots ,{u_n};\sigma _1^2,\sigma _2^2 \cdots ,\sigma _n^2$$](http://latex.codecogs.com/png.latex?%5Cfn_cm%20%24%24%7Bu_1%7D%2C%7Bu_2%7D%2C%20%5Ccdots%20%2C%7Bu_n%7D%3B%5Csigma%20_1%5E2%2C%5Csigma%20_2%5E2%20%5Ccdots%20%2C%5Csigma%20_n%5E2%24%24)
+ - 计算`p(x)`,若是`P(x)<ε`则认为异常，其中`ε`为我们要求的概率的临界值`threshold`
+
+
 
   [1]: ./images/LinearRegression_01.png "LinearRegression_01.png"
   [2]: ./images/LogisticRegression_01.png "LogisticRegression_01.png"