np.dot usage

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• For vector:

$u.dot(v)=|u|*|v|*cos \theta$
point value by seeking out a
* corresponds to multiplication by multiplying each element
may benp.dot(u,v), it may be written asu.dot(v)

Caution: the * operator will perform an elementwise multiplication, NOT a dot product:

• For matrix:

A.dot(B), Denotes the matrix multiplication, a matrix is ​​obtained. (Row vector A $m×n$ column vector of B and $n×k$ , respectively, do dot dot, end up with a matrix $m×k$ . )
A*BRepresents a multiplication element,

Caution: NumPy’s * operator performs elementwise multiplication, NOT a matrix multiplication

Point multiply and multiply * the meaning and role of unity.

• * Take boardcasting trigger mechanism of python

‘

import numpy as np
a = np.array([1,2,3])
b = np.array([2])
print(a*b)

[2 4 6]

 c = np.array([1,2,3,4])
 print(a*c)


 Traceback (most recent call last):File "<stdin>", line 1, in <module>ValueError: operands could not be broadcast together with shapes (3,) (4,)