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I have a question regarding the second skip connection in ResNet.

Here is a part of the image of the architecture as it was presented in the paper:

first two skip connections

As I understand the output of the pool layer gets skipped two conv layers and then gets added to the output of the second 3x3 conv layer 64 (first arrow).

My question is about the contents of the second arrow. Does it contain:

  1. Only the output of the second 3x3 conv layer 64?
  2. Or the output of the second 3x3 conv layer 64 + output of the pool layer?

It is sadly not discernible if the second arrow starts behind the end of the first arrow or before the end of the first arrow.

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    $\begingroup$ Second option I believe $\endgroup$ – Łukasz Grad Aug 3 '18 at 16:19
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It's the second option. It's easier to think of Resnet in terms of residual blocks. In this case each block is a pair of 3x3 convolutions (and sometimes a 1x1 down/up sampling in larger resnets). So each block has an input and output. The input is always linked to the output via addition. So the next block receives the output of the previous block, which will be the sum of the last 3x3 output plus the input from the previous block.

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