Run a model but simultaneous equations involving

[Kolakari]

Hi,

I'm currently trying to run the model but i always got a «simultaneous equations involving» problem. I'd seen simultaneous equations forum but none of them help for the moment. Anyone know how to solve it pls? Thank u

[tomfid]

You have the Type for your stocks set to Auxiliary.

If, for example, you change the type of Population to Level, and enter an initial value, that eliminates the simultaneity. I think the other errors are similar.

[Kolakari]

You're right. The model is ok now but now i have another units check problem . I must check the type for all my stocks again cause i don't understand very well this part of vensim. You help me a lot. Thank you very much

[Kolakari]

I HAVE another question about this equation : INTEG. It's said for example that INTEG (R,N) = Performs numerical integration of R starting at N (defines a Level). So i would like to know the meaning of «,» in the equation ? How is the development?

[tomfid]

https://www.vensim.com/documentation/euler.htm

[Kolakari]

I'm sorry guys but i'm back again. The model is correct but the units still missmatching..
I tried to understand the way to write the INTEG equation but i can't take off the time (week). When i made some researches about it i found that : INTEG (rate, initial value) a Numerical INTEGration is INTEG ( unit / time, unit ) --> unit
The units of the integral must be the same as the units of the initial condition. The rate must have the same units, divided by the units of TIME STEP. Here you have an example of what the software is saying
Gisement =
INTEG( Roches extraites
+ ( Stériles 1
/ Masse ouvrière affluente ) ,
Stériles 1 )
Gisement --> Tonnes/Habitants
Roches extraites --> Tonnes/Habitants
Stériles 1 --> Tonnes
Masse ouvrière affluente --> Habitants

Analysis of units error:
Units missmatch in INTEG
Roches extraites
+ ( Stériles 1
/ Masse ouvrière affluente )
Has Units: Tonnes*Week/Habitants
Stériles 1
Has Units: Tonnes

I would like to know how to write the equation please or if it's not the problem, what is the problem about my model
Thank you a lot

[Administrator]

I think it might be better if you take a step back and do a simple tutorial in Vensim. The model you have uploaded has rates as flows, and flows as rates.

On this page you will find a really good Vensim PLE tutorial.
http://www.public.asu.edu/~kirkwood/sysdyn/SDRes.htm

It will explain the differences between stocks and flows and hopefully help you see exactly where you are going wrong.

[Kolakari]

If you think so, i must. thank you