This quantity is a slightly simplified version of the WTMAD-2 indicator
introduced by Goerigk et al. \cite{goerigk_look_2017} to rank functionals based on the
performance on the GMTKN55 database. On the statistical standpoint, wMUE is the average of a slightly modified coefficient of
variation for each subset \(\left( m\text{CV}_i=\text{MUE}_i / \left|\overline{\Delta \text{E}}\right|_i \right)\) where the standard deviation is replaced by the mean unsigned error of each subset