In my previous post:
I used the Greek lowercase letter mu to refer to the mean size of the quantum dots (the 3 or 4 nm face-value). This is common practice in statistics.
I used x to refer to the specific quantum dot's size, which absorption coefficient A is also a function of. Hence A(x) and Ai, which is the ith absorption coefficient when x is the variable you are counting by.
I used the Greek lowercase lowercase sigma to represent the standard deviation of the quantum dot population. (Also common practice in statistics).
S is an arbitrary variable I assigned myself to simplify computational steps for my programming. S will depend on the sigma accuracy (i.e. 3 or 5 or 6 sigma?).
If you have any clarification questions, please ask! :-)