【机器学习】 00：准备工作Numpy

Numpy是什么

numberical 和 python
功能强大的python库
主要作用：

• 执行数学任务
• 处理图像
• 矩阵数值计算

安装

参考教程
下载网址

应用实例

3、矩阵数学运算

1. 生成随机数组random.rand(4,4)
2. 将数组转化为矩阵mat()
   注：生成随机矩阵就可以mat(random.rand(4,4))
3. 矩阵求逆randMat.I
4. 创建单位矩阵eye(n)
5. 矩阵乘法randMat*invRandMat
   注：下边代码中，矩阵和它的逆相乘按理来说应该是单位矩阵，但是由于计算机计算有误差，所以计算出来并不是，可以myEye-eye(4)得到误差值

Traceback (most recent call last):
  File "E:/Python/TestNumpy.py", line 1, in <module>
    import numpy as np
ModuleNotFoundError: No module named 'numpy'
>>> from numpy import *
>>> random.rand(4,4)
array([[0.10158214, 0.3719441 , 0.94063777, 0.50643896],
       [0.92600614, 0.77236761, 0.35572363, 0.99252495],
       [0.58464786, 0.10804458, 0.67350135, 0.87358246],
       [0.32934685, 0.2607976 , 0.72263533, 0.31676123]])
>>> randMat = mat(random.rand(4,4))
>>> randMat.I
matrix([[ 1.02749897, -2.40507528, -0.33632994,  1.27810379],
        [ 0.05177492,  2.54948785, -0.10568138, -1.17175427],
        [-2.58994448,  1.43275664,  0.68643284,  1.57925206],
        [ 0.0971614 ,  0.62072199,  1.08438911, -0.98672751]])
>>> invRandMat = randMat.I
>>> randMat*invRandMat
matrix([[ 1.00000000e+00,  5.28210783e-17, -7.54562791e-17,
          1.69183312e-16],
        [-2.02484111e-16,  1.00000000e+00,  4.91238539e-18,
         -2.15480015e-17],
        [ 2.86544104e-17,  2.51922955e-16,  1.00000000e+00,
          1.57562566e-16],
        [ 2.26452988e-16,  4.92101953e-17, -3.25806708e-17,
          1.00000000e+00]])
>>> myEye = randMat*invRandMat
>>> myEye - eye(4)
matrix([[ 0.00000000e+00,  5.28210783e-17, -7.54562791e-17,
          1.69183312e-16],
        [-2.02484111e-16,  0.00000000e+00,  4.91238539e-18,
         -2.15480015e-17],
        [ 2.86544104e-17,  2.51922955e-16,  0.00000000e+00,
          1.57562566e-16],
        [ 2.26452988e-16,  4.92101953e-17, -3.25806708e-17,
          2.22044605e-16]])
>>> 

参考文献

1. 《机器学习实战》