a problem regarding the simulated values for stocks and flow

LBD · Post by **LBD** » Wed Mar 22, 2006 7:05 pm

Bob,

I am having problems with the results that Vensim shows for the stocks. for some reason instead of simply subtracting the outflow from mthe inflow to give the values for the stock, the results i get are that it adds up the inflow, outflow and the stcock value for the previous month and shows it as a result for the calculation for the current month. I am attaching an excel file, with the results that i have got and also the equation for the stock. Any information would be appreciated.

Lisa.

Lee Jones · Post by **Lee Jones** » Thu Mar 23, 2006 10:02 am

Lisa,

I have had a quick look at the results and they are correct. The value of a stock at any point in time is it's previous value plus the net of inflow/outflow in the intervening period. So, the first calculation takes the initial stock value of 3,800, adds the 3,800 notified students (inflow) and removes the 380 fall outs (outflow) to calculate the new stock value of 7,220 (3,800 + 3,800 - 380). And so on.

Lee

LBD · Post by **LBD** » Thu Mar 23, 2006 1:54 pm

Thank you for your help. If that is the case with stocks and flows, is it possible or is there a way so as not to include the previous value of the stock to the current one and just have the difference of the flows?

LBD · Post by **LBD** » Thu Mar 23, 2006 2:28 pm

Thanks Lee,

I figured out what to do, to get the values that i need.