Friday, January 6, 2017

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.







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.


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