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Track of stock inflow
Posted: Wed Aug 20, 2003 9:01 am
by Robbert
I would like to track the build up in a stock within a model. Because other parts of my model depend on it.
E.g.: Every month I have a new number of members coming in. Say the model runs over 12 months. Is it possible to have one single stock that tracks the total number of members while other parts of the model use the number of members signed up at t=3?
Thanks,
Robbert
Posted: Wed Aug 20, 2003 9:09 am
by Lee Jones
Welcome to the forum Robbert.
I am not entirely sure I understand the question really. Obviously, the stock will track the cumulative members added since the start of the simulation, so long as you do not drain the stock with leavers.
In your stock and flow diagram, if you have to have new members joining and they go on to some other state (left, active, inactive or whatever), then simply add a second stock to accumulate the total members added since time 0.
If you wish to record the rate at which members were added at time = 3 (which is what I think you are saying), then use a sample_if_true to capture the figure at time=3. I am not sure what use it would be to you though!
Post some more details and perhaps we could get to the bottom of this.
Lee
Posted: Wed Aug 20, 2003 9:55 am
by Robbert
Lee,
Thanks for the welcome and fast reply.
I rephrased the question with an example to clarify what I am trying to achieve.
Structure: stock of members, fed by the rate on new members arriving every month.
Problem: at time T, I wish to know what the number of members by their age of membership i.e how many members arrived at time T, time T-1, T-2…
Example:
Inflow membership is random over a period of 50 months:
Number of members builds up in 1 single stock.
Revenue depends on the duration of membership. Assume fees per month depend on age of membership: 0-6 months $ 15, 6-12 months $ 20, 12 months+ $ 10.
To build my revenue model I need to know the age of the members in my stock.
Is this possible without having to model different stocks for each age group?
Regards,
Robbert
queue fifo
Posted: Wed Aug 20, 2003 10:20 am
by Wilson
Robbert,
Have a look at using a FIFO queue as the stock of members. You can then use the function QUEUE AGE IN RANGE() .This will return the number or elements in a queue at least as old as minage and not older than maxage
If you have "leavers" though the assumption would be that the older members leave first, which might not be appropriate in your case.