02. 导数与梯度矩阵运算性质科学计算库numpy

Posted 2020-10-26 years4nancy

一、数学基础

二、numpy

 

 

 

一、数学基础

关键字：求导、偏导、梯度、复合函数求导链式法则

             矩阵的转置、矩阵加减、矩阵乘法【矩阵乘法不满足交换律】

 

二、numpy

#coding:utf-8

import numpy as np

print np.__version__

 

# 1- create narray

array = np.array([1,2,3],dtype=np.uint8)

print "array:",array

 

# 2- zeros

mat1 = np.zeros((2,3)) #(2,3) tuple

print "mat1:",mat1

 

# 3- 高维矩阵

mat2 = np.zeros((1,2,3,4))

print mat2.shape

print mat2.size

 

# 4- 标准矩阵运算

# (1) 标量与矩阵相乘

scalar = 2

mat = np.ones((2,3))

mat3 = scalar * mat

print "mat3:",mat3

# (2) 矩阵转置 mat.T

mat = np.zeros((2,3))

tmat = mat.T

print mat.shape,tmat.shape

mat4 = np.array((1,2,3))

print "mat4:",mat4

tmat4 = mat4.T

print mat4.shape,tmat4.shape

# (3) 矩阵的加法

print "add--------------------"

mat1 = np.array([[1,2],[3,4]])

mat2 = np.zeros((2,2))

mat3 = mat1 + mat2

print "mat3:",mat3

# (4) 矩阵的乘法

print "multi------------------"

mat1 = np.array([[1,2],[3,4]])

mat2 = np.ones((2,2))

mat3 = mat1.dot(mat2)

print "mat3:",mat3