Numpy Basic dot matrix product

• Python: 3.8.11
• Numpy: 1.20.1
• OS: Ubuntu Kylin 20.04
• Conda: 4.10.1
• Jupyter lab: 3.1.4

Code sample

import numpy as np
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a = np.array([[1.2.3.4], [5.6.7.8]])
b = np.array([[1.2.3], [4.5.6], [7.8.9], [10.11.12]])
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a

array([[1.2.3.4],
       [5.6.7.8]])
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b

array([[ 1.2.3],
       [ 4.5.6],
       [ 7.8.9],
       [10.11.12]])
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a.shape,b.shape

((2.4), (4.3))
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The number of columns in the first matrix is the same as the number of rows in the second matrix
np.dot(a,b)

array([[ 70.80.90],
       [158.184.210]])
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np.dot(b,a)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-69-e6bd3a7b39a0> in <module>
----> 1 np.dot(b,a)

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

ValueError: shapes (4.3) and (2.4) not aligned: 3 (dim 1) != 2 (dim 0)
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The source code to learn

help(np.dot)

Help on function dot in module numpy:

dot(...)
    dot(a, b, out=None)
    
    Dot product of two arrays. Specifically,
    
    - If both `a` and `b` are 1-D arrays, it is inner product of vectors
      (without complex conjugation).
    
    - If both `a` and `b` are 2-D arrays, it is matrix multiplication,
      but using :func:`matmul` or ``a @ b`` is preferred.
    
    - If either `a` or `b` is 0-D (scalar), it is equivalent to :func:`multiply`
      and using ``numpy.multiply(a, b)`` or ``a * b`` is preferred.
    
    - If `a` is an N-D array and `b` is a 1-D array, it is a sum product over
      the last axis of `a` and `b`.
    
    - If `a` is an N-D array and `b` is an M-D array (where ``M>=2``), it is a
      sum product over the last axis of `a` and the second-to-last axis of `b`::
    
        dot(a, b)[i,j,k,m] = sum(a[i,j,:] * b[k,:,m])

......
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Learning to recommend

• Python documentation – English
• Python documentation – Chinese
• Python code PEP
• Google version of the Python specification
• Python source code
• Python PEP
• Optimal kirin
• The nuggets platform
• Gitee platform

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