Norm knowledge points of machine learning

1-norm:

||x||_1 = \sum_{i=1}^N|x_i|, that is, the sum of the absolute values ​​of the vector elements, matlab calls the function norm(x, 1)



2-norm:

||\textbf{x}||_2 =\sqrt{\sum_{i=1}^Nx_i^2}, Euclid norm (Euclidean norm, commonly used to calculate the length of the vector), that is, the square sum of the absolute values ​​of the vector elements and then the square root, matlab calls the function norm(x, 2).

\infty- Norm: ||\textbf{x}||_\infty = \max_{i}|x_i|, that is, the maximum value in the absolute value of all vector elements, matlab calls the function norm(x, inf).


-\infty- Norm:||\textbf{x}||_{-\infty}=\min_i|x_i|

, that is, the minimum value among the absolute values ​​of all vector elements, and matlab calls the function norm(x, -inf).


p-norm: ||\textbf{x}||_p = (\sum_{i=1}^N|x_i|^p)^{\frac{1}{p}}
, that is, the 1/p power of the sum of the absolute value of the vector elements to the p power, matlab calls the function norm(x, p).


Other matrix norm, etc., refer to the link below


Link: https://www.zhihu.com/question/20473040/answer/102907063

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