Consider the following variable $e$, which is a $mn\times 1$ vector, where $m$ is number of countries and $n$ is number of sectors (for instance).
I want to sum over the vector, but how do I write that in a formal way? Can I use the following notation:
$\sum^{mn}_{i=1}e_i\quad\quad i=\{1,\dots,mn\}$