I’ve started to learn about neural networks recently and I can’t find the answer to this question.
Let’s assume there’s a neural network (fig. 1) 
So if the loss function is: 
and the derivative 
is: 
if I want to use this to find 
what k and l (well there’s only one neuron with index l here, but what if there would be more?) should i use in 
and 
?
Sorry if I failed to explain my problem. If something isn’t clear please ask in comments.
