Notes | numpy-09 Broadcast

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#  radio broadcast (Broadcast) yes  numpy  For different shapes (shape) How to do the numerical calculation of the array ,  Arithmetic operations on arrays are usually performed on the corresponding elements 
#  If two arrays  a  and  b  The same shape , The meet  a.shape == b.shape, that  a*b  The result is that  a  And  b  Array corresponding bit multiplication . This requires the same dimension , And the length of each dimension is the same 
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import numpy as np

a = np.array([1, 2, 3, 4]) # 4r1c
a
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b = np.array([10, 20, 30, 40]) # 4r1c
b
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c = a * b
c
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#  When in operation  2  The shapes of arrays are different ,numpy  Will automatically trigger the broadcast mechanism 
import numpy as np

a = np.array([
    [0, 0, 0],
    [10, 10, 10],
    [20, 20, 20],
    [30, 30, 30]
])
a # 4r3c
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b = np.array([1, 2, 3])
b # 1r3c
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""" a Row index 0 0+1=1 0+2=2 0+3=3 a Row index 1 10+1=11 10+2=12 10+3=13 a Row index 2 20+1=21 20+2=22 20+3=23 a Row index 3 30+1=31 30+2=32 30+3=33 """
a + b #  take b Bring in the a | a Column correspondence of b The line of  |  When calculating, it will be calculated in sequence with the same number of edges 
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bb = np.tile(b, (4, 1)) #  repeat  b Dimensions of  | 1  Repeat in the vertical direction  2  Repeat horizontally  | 4  repeat 4 Time 
bb
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a + bb #  Equate to  a + b
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"""  The rules of broadcasting :  Let all the input arrays look to the array with the longest shape , The insufficient parts in the shape are all preceded by  1  A filling .  The shape of the output array is the maximum value on each dimension of the shape of the input array .  If a dimension of the input array has the same length as the corresponding dimension of the output array, or its length is  1  when , This array can be used to calculate , Otherwise mistakes .  When the length of a dimension of the input array is  1  when , The first set of values on this dimension is used when calculating along this dimension   Simple understanding ： For two arrays , Compare each of their dimensions （ Ignore if one of the arrays has no current dimension ）, Satisfy ：  Arrays have the same shape .  The value of the current dimension is equal .  One of the values of the current dimension is  1.  If the conditions are not met , Throw out  "ValueError: frames are not aligned"  abnormal  """