Accumulation

[Tom]

Hi there,

new to this forum, and not really an advanced Vensim user. But I am trying to accumulate the results of an equation (no raw data), and fail to do so. I am calculating sales per year, and would like to add them up according to a lifetime t of the sold item. Example: lifetime t = 3 years, starting year is 1990:

1990 1991 1992 1993 1994 1995
sales 1 2 3 4 5 6
Cum. sales 1 3 6 9 12 15

Any help would be greatly appreciated!

Thanks
Tom

[Administrator]

Usually cumulation is done using the integ function. Be sure to enter dimensions for your equations.

Hope this helps,

Tony.

[tomfid]

What you're specifically after would be something like the following, I think:

Cum Sales = INTEG( sales - outflow, 0 )
outflow = DELAY FIXED( sales, time to cumulate, 0)
time to cumulate = 3

The continuous version would have
outflow = Cum Sales/time to cumulate

Tom