Optimization Algorithms, Optimization Techniques, Machine Learning, Deep Learning, Convex Optimization.
the optimal weights (w_j) for which the MSE Loss function (given in eq. 3 above) has minimum value, for a GIVEN X, Y data (refer to very first the table at the start of the article). L(w_j) represents the MSE Loss, which is a function of the model weights, not X or Y. Remember X & Y is your DATA