Correct L2 regularization sequence?

Question

Machine learning

The neural network began to retrain, regularization is required, I can’t understand at what stage this function is used.
At the stage of finding the gradient? New to this topic.

Answer 1

Regularization is applied in the backpropagation step.
In simple terms - you want to avoid very large weights for some neurons (aka overfitting). The more weight a certain neuron has, the more regularization for that neuron.
Picture from the Internet for clarity. I hope it helps to understand