In my previous post, I described various (potentially non-smooth) functions that have quadratic (and thus smooth) variational formulations, a possibility that I referred to as the η-trick. For example, in its simplest formulation, we have \( \displaystyle |w| = \min_{ \eta \geq 0} \frac{1}{2} \frac{w^2}{\eta} + \frac{1}{2} \eta\). While it seems most often used for…