# Summation notation for time series

I need to add together the results of a function for four consecutive years prior to the start of a project. The function is calculated for individual years. It is (10 × (A + B + C) ÷ D). Each year has a set of values for the variables A, B, C, D. So maybe it is something like

sum (n=1..4, (10 × (At-n + Bt-n + Ct-n) ÷ Dt-n))

whereby I mean t=0 is the point in time when a project starts and "n" is the number of years prior to t=0 and would be from 1 to 4. I attempted to use the plain text version of sigma notation (summation notation) above because using equation editors is difficult with voice recognition software. Would you please help me get my notation correct? I don't really know what I am doing… any assistance would be greatly appreciated.

## 1 Answer

If I understood your question correctly, then I would suggest saying something along the lines of the following:

We will use subscripts to denote the number of years prior to 2014, so that $B_3$ is the value of $B$ for the year 2011, etc.

The quantity we are interested in is $$\sum_{n=1}^410\frac{A_n+B_n+C_n}{D_n}$$

You can right click each math expression and click "show math as TeX" commands to see the code which, when typed between dollar signs, will produce the expression here, on mathbin, or somewhere else accepting TeX-style input.

• That's fantastic thank you! I think your answer is right for my purpose and thanks for advice about using the equation notation :) – Stuartzz Mar 10 '14 at 22:56
• @Stuartzz I'm glad it was helpful. If you feel my answer was what you were looking for, you can accept it to let people know the question has been answered. – Mark S. Mar 11 '14 at 0:25