NumPy基础

Posted 2020-10-20 hellojack

导入numpy

from numpy import *

生产4*4随机数组

random.rand(4,4)

Out[12]: 
array([[ 0.62906836,  0.68003924,  0.23429915,  0.33934942],
       [ 0.16138277,  0.50783913,  0.81208135,  0.73155125],
       [ 0.03198512,  0.06235509,  0.84971987,  0.40201476],
       [ 0.60382374,  0.23330463,  0.19498809,  0.49371285]])

数组转换为矩阵

randMat = mat(random.rand(4,4))

求矩阵的逆

randMat.I

Out[14]: 
matrix([[-1.24839656,  1.95298502,  0.13778596, -0.55000061],
        [ 0.47513857, -1.21734464,  1.22431076, -0.99281312],
        [ 1.43191954, -0.30628506, -0.22557989,  0.27913877],
        [ 0.33002468, -0.95613875, -0.03658288,  1.42874831]])

计算矩阵与其逆矩阵相乘的结果

randMat * invRandMat

matrix([[  1.00000000e+00,  -9.71445147e-17,   8.20198943e-17,
           7.97972799e-17],
        [ -8.32667268e-17,   1.00000000e+00,   9.28077060e-17,
           1.11022302e-16],
        [  0.00000000e+00,  -4.44089210e-16,   1.00000000e+00,
           0.00000000e+00],
        [  0.00000000e+00,  -1.11022302e-16,  -6.93889390e-18,
           1.00000000e+00]]

结果应该是单位矩阵，除了对角线元素是1，其他元素应该全是0。实际输出结果中，矩阵还留下了许多非常小的元素，这是计算机误差产生的结果，计算误差值：

myEye = randMat*invRandMat

myEye - eye(4)#函数eye(4)创建4*4的单位矩阵

Out[18]: 
matrix([[  0.00000000e+00,  -9.71445147e-17,   8.20198943e-17,
           7.97972799e-17],
        [ -8.32667268e-17,   0.00000000e+00,   9.28077060e-17,
           1.11022302e-16],
        [  0.00000000e+00,  -4.44089210e-16,   2.22044605e-16,
           0.00000000e+00],
        [  0.00000000e+00,  -1.11022302e-16,  -6.93889390e-18,
           2.22044605e-16]])