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My question is in regards to an MIT course example.

NN Schematic

The instructor delves into the backpropagation of this simple NN.

NN with derivative chain and equations

I have two questions.

  1. Why do we seem to disregard the weights of the second layer (in blue)?
  2. The red circle, should this not be $\partial y_2$ (followed by $\frac{\partial y_2}{\partial P_3}$)?
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  • Why do we seem to disregard the weights of the second layer (in blue)? -----because activation function is after that block, so differential with the o/p y is as good as with the weight.

  • The red circle, should this not be ∂y2 (followed by ∂y2∂P3)? -----y2 and y1 is the o/p of the same block i.e. both must be same

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  • $\begingroup$ Wow thanks, I feel silly now. Thanks again! $\endgroup$
    – Shinobii
    Oct 20, 2019 at 17:25

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