Past exam of the mathematics course of the University of Cambridge / 2021 / iii / Paper 218 / 4 / d / Solution

For all weights and biases collected in $\vartheta$, fitUse backpropagation with stochastic gradient descent or a modern adaptive variant, treating the absolute-value derivative at zero as stated. Select $({\lambda }_1,{\lambda }_2)$ by validation or cross-validation and refit using the selected pair.