How to express matrix vector multiplication in Java

Vector

Dot product
Formula: a ·b = |a| * |b| * cosθ The dot product is also called the inner product and quantity product of vectors. It is a The product of a vector and the length of its projection onto another vector; is a scalar quantity. The dot product reflects the "similarity" of two vectors. The more "similar" the two vectors are, the greater their dot product is.

Example: If vector a=(a1,b1,c1), vector b=(a2,b2,c2)
Vector a·Vector b=a1a2 b1b2 c1c2

Cross product
Formula: a × b = |a| * |b| * sinθ Cross product is also called the outer product and vector product of vectors. The result is a vector
Modulus length: |vector c|=|vector a×vector b|=|a||b|sin
Direction: The direction of the vector product of a vector and b vector is the same as this The two vectors are perpendicular to the plane and obey the right-hand rule.
Example
Vector a a2b1) (The main diagonal is positive)
(i, j, k are the unit vectors of the three mutually perpendicular coordinate axes in the space)

Matrix

Element multiplication: np .multiply(a,b)

Matrix multiplication: np.dot(a,b) or np.matmul(a,b) or a.dot(b) or directly use a @ b !

Only attention :*, overloaded in np.array for element multiplication, and in np.matrix for matrix multiplication!

Very good link

import numpy as np
a=np.array([[1,2],[3,4]])#生成数组矩阵b=np.array([[2,2],[1,3]])print(np.dot(a,b))>>[[ 4  8]
  [10 18]]

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