python numpy array 与matrix 乘方

编程语言 waitig 1年前 (2017-04-18) 1272℃ 百度已收录 0评论

数组array 的乘方（**为乘方运算符）是每个元素的乘方，而矩阵matrix的乘方遵循矩阵相乘，因此必须是方阵。

2*3的数组与矩阵

>>> from numpy import *

>>> import operator

>>> a = array([[1,2,3],[4,5,6]])

>>> a

array([[1, 2, 3],

       [4, 5, 6]])

>>> m = mat(a)

>>> m

matrix([[1, 2, 3],

        [4, 5, 6]])

>>> a ** 2

array([[ 1,  4,  9],

       [16, 25, 36]])

>>> m ** 2

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

  File "D:\anaconda\lib\site-packages\numpy\matrixlib\defmatrix.py", line 356, in __pow__

    return matrix_power(self, other)

  File "D:\anaconda\lib\site-packages\numpy\matrixlib\defmatrix.py", line 173, in matrix_power

    raise ValueError("input must be a square array")

ValueError: input must be a square array

>>> 

（mat()函数把array转化为matrix）

3*3的数组与矩阵

>>> A = array([[1,2,3],[4,5,6],[7,8,9]])

>>> A

array([[1, 2, 3],

       [4, 5, 6],

       [7, 8, 9]])

>>> M = mat(A)

>>> M

matrix([[1, 2, 3],

        [4, 5, 6],

        [7, 8, 9]])

>>> A ** 2

array([[ 1,  4,  9],

       [16, 25, 36],

       [49, 64, 81]])

>>> M ** 2

matrix([[ 30,  36,  42],

        [ 66,  81,  96],

        [102, 126, 150]])