Ventana software support forum

Hi,
When a simple model is created in Vensim, with just one stock and inflow and outflow.
When we want to insert the formula of the given stock, in the part of variables you find the inflow name, the outflow and stock name. why is there the stock variable name? it does not make sense.
thx

Do you mean where "Causes" is listed? The stock directly influences the value of itself at the next time step (so it is a cause).

Hi

It is not only an implicit causes that does not appear in the equation.
There are many cases where you need to put the stock in the equation.
For instance if you go to the Vensim help and index and ask for the smooth function.
You will see a stock and flow formulation of the smsooth function where the level is explicitly included.
expected demand =INTEG((demand-expected demand)/ time to form expectations,demand)

Regards.

JJ

The stock name is there because it is a valid input. For example, an alternative implementation of a SMOOTH is:

smoothed input = INTEG( (input-smoothed input)/smoothing time, initial input )

However ... it is true that if you do this, your diagram is likely to break standard stock-flow diagramming conventions. Sometimes that's useful.

thanks for all answers I got it
Best wishes