线性回归 Linear Regression

什么是线性回归?

y = f(x), a function that representing the relationship between input x and output y. The Function we used here is the general Linear Function.

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常用的线性回归函数

1.多项式函数（Polynominal Function）

(graph from wikipedia)

Comments:

1. most common function, fitting to most cases in life.

2. y is ranged from .

3. x is ranged from 

4. one x only has one y. (say, otherwise, for , one x has 2 different y)

2.sigmoid 函数（Sigmoid Function）

(graph from wikipedia)

Comments:

1. y is ranged from 0 to 1 (so it can represent the pobability, that‘s why the logistic regression uses this function to fitting the relationship between the prob and input)

2.x is ranged from 

2.RBF 函数（Radial Basis Function）

(graph from wikipedia)

Comments:

1. radially symmetric

2. wide used (e.g. Gaussian Prob Density)

2017-08-15

线性模型的效果受线性公式影响， 应当选择和当前应用项目匹配的函数。