# Sigma notation for time

Discussion in 'Education' started by Shane Van Dalsem, Oct 8, 2018.

1. ### Shane Van DalsemGuest

I need to convert a sigma notation to change the number of observation from a set number to having an ending day as a variable. The language for the first notation is the sum of $S^2$ for each day, t, from Day -5 to Day 5. The language for the second notation is the sum of $S^2$ for each day, t, from Day -5 through day t.

The original notation is $$\sum_{t=-5}^5 S^2 (A_t)$$

I want to switch the end observation from +5 to day t. My first inclination was to use $$\sum_{t=-5}^t S^2 (A_t)$$ but that doesn't seem right. Should I switch the end day to a different variable or the t to to a different variable? Thank you for your help.