Hi, I tried to reproduce the code from chapter 9 from the memory and noticed, that the calculation of the error in chapter 9 for batch gradient decent is different from the calculation in chapter 8.

In chapter 8 it is calculated as follows:

layer_2_delta = (labels[batch_start:batch_end]-layer_2)/batch_size

In chapter 9 it is calculated in the following way:

layer_2_delta = (labels[batch_start:batch_end]-layer_2) / (batch_size * layer_2.shape[0])

I was not able to find any explanation for the reasons, why delta calculation is different, but the results obtained are as well differ as well.
It would be good to get the clarification for this part of code

I agree. Dividing the layer_2_delta by layer_2.shape[0] is not explained anywhere in the text. I think ultimately what is happening is that all of these eventually get absorbed in the alpha value. Take a look at alpha it is 2. Your overall point is correct though, this should be explained given that the book is supposed to be accessible to anyone.