import numpy as np
x = np.arange(20)
x = np.reshape(x, (4,5))
dW = np.zeros(x.shape)
dWhy = dW
dW += np.sum(x)
dWhy += x
Why do the two methods results in the same result (dW = dWhy), when
dW = dW + np.sum(x)
dWhy = dWhy + x
does not?
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1 Answer
Because dWhy = dW makes them the same array. += is not a redefinition (reassignment), it changes the values inplace.
dW += np.sum(x) # affects both since they are the same object
dWhy += x # affects both since they are the same object
Unless you redefine (reassign) one of them later.
dW = dW + np.sum(x) # redefines dW
dWhy = dWhy + x # redefines dWhy
Another way to make dW and dWhy 2 different arrays that can then be changed inplace independently with += would be to define dWhy = dW.copy() at the start.
1 Comment
mozway
I would say "same object" for clarity ;)