Ventana software support forum

hi all,

me and my colleague are sitting over a model for hours... we could need help please.

we are trying to solve one of sterman's models concerning product awareness, cause we we're philosophising about our product, we are planing to launch, at least in our minds

the basic model is attached, we would need help to formulate mathematical correlations. what would be your next step looking at the model?

thanks in advance

alright, v2 is here.

our problem now is, we get an 'simultaneous equations involving' error involing 'advertising'.

we do not really understand what this means, altough we read the example solving this problem in the manual.

any help understanding this model?

This is a classic simultaneity - Sterman's book is probably a better source for understanding it than the manual

In orer to compute you need to know market share which depends on advertising which depends on revenue which depends on sales.

In real life there is a delay from revenue to advertising and from advertising to market share.

I would recommend reading a bit more of Sterman's book - I am pretty sure he covers models like this.

thanks.
yea, i guess we are on the right way.

our last step would be inserting a delay_fixed.
how would you do that, as you described it, since on the right hand of the equation theres only room for a delay expression and not any other formulas.

I would recommend either a SMOOTH function or an explicit first order exponential delay (see Sterman).

But in any case the delay should stand by itself eg

expected revenue = INTEG((revenue - expected revenue) / time to perceive revenue,iniital expected revenue)

bob, thanks a lot for your help.
i guess we managed to finish it the way it should be.

regards

Hi Leonardo,

In your model - for the reinforcing loops R1 and R2, there are no stocks. Every loop needs to have atleast one stock . Else the change is instantaneous

I feel you will need atleast one stock in each of those loops

Bob - is my thinking right on this?

Regards
Malli

Hi Mali,

Yes - sorry I didn't articulate that better in my prior post - a simultaneity is a loop without a stock.