Numpy：点积和 dot() 矩阵相乘

Posted 2021-02-05 wodexk

一、Numpy的点积和dot矩阵相乘

dot（）使用需注意：前一个矩阵的行数要与后一个矩阵的列数一致

import numpy as np
print("============点积:A*B,对应位置相乘===============")
A = np.array( [[1,1],
               [0,1]] )
B = np.array( [[2,0],
               [3,4]] )
print ("A=","
",A)
print ("B=","
",B)

print ("A*B=","
",A*B)
# A.*B =[[1*2,1*0]
#        [0*3,1*4]]
#      =[[2,0]
#       [0,4]]

print("=============dot：矩阵相乘======================")

print("-----书写格式1：A.dot(B)-----")
print (A.dot(B))   
# A.dot(B)=[[1*2+1*3,1*0+1*4]
#           [0*2+1*3,0*0+1*4]]
#        =[[5,4]
#          [3,4]]


print("-----书写格式2：np.dot(A, B)-----")
print (np.dot(A, B)) 
# A.dot(B)=[[1*2+1*3,1*0+1*4]
#           [0*2+1*3,0*0+1*4]]
#         =[[5,4]
#           [3,4]]

结果图：

 

 代码2：dot（）使用需注意：前一个矩阵的行数要与后一个矩阵的列数一致

import numpy as np
a=np.ones((1,3,5))
print(a)
b=np.ones((5,6))*3
print(b)
c=a.dot(b)

print(c.shape)
print(c)

结果图：