1. Vector norm
A norm is a function with the concept of "length". In vector space, assign a non-zero positive length or size to all vectors. Different norm, the length or size of the vector is different.
2. Several commonly used norms
(1) 1-norm
, that is, the sum of the absolute values of the vector elements
(2) 2-norm:
, Euclid norm (Euclidean norm, commonly used to calculate vector length), that is, the sum of the squares of the absolute values of the vector elements and then the square root
(3) 
- Norm:
, that is, the maximum value of the absolute values of all vector elements
(4) 
- Norm:
, that is, the minimum value among the absolute values of all vector elements
(5) p-norm:
, i.e. the sum of the absolute values of the vector elements to the p power to the power of 1/p
Reference: https://www.zhihu.com/question/20473040/answer/102907063