“…Various strategies were proposed in order to address the first question [26,27,28,29,30], but the computational cost of these methods is often high, especially when several regularization parameters have to be set. Alternatively, it has been recognized for a long time that incorporating constraints directly on the solutions [31,32,33,34,35] instead of considering regularized functions may often facilitate the choice of the involved parameters. Indeed, in a constrained formulation, the constraint bounds are usually related to some physical properties of the target solution or some knowledge of the degradation process, e.g.…”