E is just a function such that E1=1, E2=2 and so on. But my question is the part of on "arg" and "min".
1) so "arg" stands for the angle of complex number? this doesn't make any sense.
2）If I use a "min" in front of a summation, do I only take the minimum terms of the entire summation?
3) If you look understand the "min", there is "i:s_i
It looks like the sum is over the index $j$, so the terms in the sum will be $E_{i_{n-1}} + E_{i_{n-1} + 1} + \cdots + E_{i-1}$. The minimum is then taken over the index $i$, so you choose an $i$ such that the sequence, divided by the $s_i - s_{i_{n-1}}$ term, is minimal. The stuff underneath the min put additional constraints on the $i$, i.e. that $s_i$ is less than some $T$ and that the denominator is positive. I have no idea what the arg is doing. Hope this helps a bit.
Edit: As user Shaktal pointed out, it's actually the argmin function. (I hadn't heard of it before.) The formatting is just bad.