import numpy as np;
两者在创建单位矩阵上，并无区别，两者的区别主要在接口上；
np.identity(n, dtype=None)：只能获取方阵，也即标准意义的单位阵；
-
np.eye(N, M=None, k=0, dtype=<type ‘float’>)；
N : int，Number of rows in the output.（行数，必选）
M : int, optional，Number of columns in the output. If None, defaults to
N.（）- k : int, optional，Index of the diagonal: 0 (the default) refers to the main diagonal,
- a positive value refers to an upper diagonal,
- and a negative value to a lower diagonal.