Maybe this is because of my lack of mathematical maturity, but one of the most annoying aspects of mathematics in college or in applied fields (like finance and economics) is that subscripts and superscripts are under the whim of the author and thus are widely different in what they mean.
Is there a universal rulebook on subscript and superscript usage in mathematics that can allay such confusions for the reader?
As far as I am aware the most confusing situations are where indexes are on the superscripts -- is this done because putting many commas in the subscripts is messy, or is this a specific abuse of notation that should be avoided?
PS the picture comes from the Brinson Model(1985). I suppose the superscripts 'b' and 'p' are 'benchmark' and 'portfolio' but they are kind of taken to be granted instead of explained -- i.e. someone could easily just have written j,b and j,p instead, right?
It's allowed to use superscripts as indices, but usually it is done when it doesn't make sense to regard it as an exponent, such as with a vector. That seems to be the case here, as $w^b$ and $r^p$ are vectors. It still ends up being ambiguous when you take the components of the vector, but hopefully it will be stated beforehand that the superscript is an index and not an exponent.