This is almost definitely a case for "not knowing what to search for", but am interested in how to refer to the following:
For a set of $n$ reals (say non-negative), I'm interested in characterizing how "concentrated" the values are in the top few (a la Pareto $80/20$). This could be for instance for thinking about percent of total variance of top few principal components.
Is there a way to refer to this function? I'd want a single value, similar to AUROC in statistics.
Context: I'm interested in optimizing over this function as a tradeoff, similar to penalties on norms like $L^1$ or $L^0$.