Ventana software support forum

In the moment I am occupied with my diploma thesis, where I am working with Vensim. I do a flow chart, in which I want to share the value of one box in different boxes by doing the following equations:
(Fö1 = 0.15*Eisenerzvorkommen)
(Fö2 = 0.1*Eisenerzvorkommen)
(Fö3 = 0.05*Eisenerzvorkommen)
...
I want to have different parts on the right of the left box. But if I do that and I run the simulation, the result isn't that, what I expected. The value of the right boxes are increasing in a way that I can't understand. Do you understand my problem and can you solve it?
For a better understanding I sent you enclosed a picture of the important part in Vensim!
Thank you very much!

Hi -

Let me be sure I understand your equation: would you translate Eisenerzvorkommen as something like "iron ore reserves" - i.e. a stock of minerals? And Fö is presumably short for Förderung (something like mining or production, a flow)?

If so, I interpret your equations and diagram to mean that production in a particular country equals total production, multiplied by a fraction representing the share of each country in the total (your 0.15, 0.1, 0.05).

In that case, I would expect that your equations above would work properly.

However, because you've used boxes on your diagram, I would guess that you have used the "level" variable type, where you should be using an "auxiliary". That means that your equation is really Fö1 = INTEG( 0.15*Eisenerzvorkommen, 0 ) which will cause Fö1 to grow (accumulate) over time, even when Eisenerzvorkommen is constant.

The solution is to change the variable types to "Auxiliary". You can still preserve the box graphics on your diagram. That would be nonstandard usage for system dynamics, but perhaps fine for other purposes. You can change the appearance of any variable by clicking with the right mouse button, or by using the settings in the bottom toolbar.

Tom

That's it!
Thanks a lot for your help!