numpy求矩阵范数 ||x|| (np.linalg.norm)

参考：https://www.cnblogs.com/devilmaycry812839668/p/9352814.html

import numpy as np
x=np.array([[0, 3, 4], [2, 6, 4]])
y=np.linalg.norm(x, axis=1, keepdims=True)
z=x/y