np.array()中， “ * ”，np.dot(),np.multiply(),np.matmul()和@的用法

import numpy as np

a=np.array([[1,2],[3,4]])
b=np.array([[1,2],[3,4]])
c=np.array([1,3])
d=np.array([0,1])
e=np.array([[2,1]])
           

(1) * 的用法，對應位置元素相乘; multiply對應元素相乘，類似 *

print(a*b)#對應位置元素相乘
print(np.multiply(a,b))#對應位置元素相乘
           

[[ 1  4]
 [ 9 16]]
[[ 1  4]
 [ 9 16]]
           

print(a*c)
print(np.multiply(a,c))
           

[[ 1  6]
 [ 3 12]]
[[ 1  6]
 [ 3 12]]
           

print(c*d)
print(np.multiply(c,d))
           

[0 3]
[0 3]
           

print(d*e)
print(np.multiply(d,e))
           

[[0 1]]
[[0 1]]
           

(2) dot 行對列，對應元素相乘再相加,@,matmul三者相似

a=np.array([[1,2],[3,4]])
b=np.array([[1,2],[3,4]])
c=np.array([1,3])
d=np.array([0,1])
e=np.array([[2,1]])
           

print(np.dot(a,b))#行對列，對應元素相乘再相加求和（矩陣乘法）
print([email protected])
print(np.matmul(a,b))

           

[1,2] [1,2]

[3,4] [3,4]

計算過程為 :

[1x1+2x3 1x2+2x4]

[3X1+4x3 3x2+4x4]

[[ 7 10]
 [15 22]]
[[ 7 10]
 [15 22]]
[[ 7 10]
 [15 22]]
           

print(np.dot(a,c))
print([email protected])
print(np.matmul(a,c))
           

[ 7 15]
           

print(np.dot(c,d))
print([email protected])
print(np.matmul(c,d))
           

3
           

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-88-a4f728f79257> in <module>
----> 1 print(np.dot(d,e))


<__array_function__ internals> in dot(*args, **kwargs)


ValueError: shapes (2,) and (1,2) not aligned: 2 (dim 0) != 1 (dim 0)
           

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-90-afe09a6d039d> in <module>
      1 #兩者都報錯
----> 2 print(np.matmul([email protected]))


ValueError: matmul: Input operand 1 has a mismatch in its core dimension 0, with gufunc signature (n?,k),(k,m?)->(n?,m?) (size 1 is different from 2)
           

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-91-b9f371cba1e1> in <module>
----> 1 print([email protected])


ValueError: matmul: Input operand 1 has a mismatch in its core dimension 0, with gufunc signature (n?,k),(k,m?)->(n?,m?) (size 1 is different from 2)