Help with a sigmoidal behaviour in a stock variable

[Nu_user]

Hi colleagues,
I request your assistance in modeling sigmoid behavior in an accumulated variable (a stock variable without outflows).
I need to model an accumulated variable with sigmoid behavior to incorporate it into a model that dynamically emulates its maximum.
I searched the forum for previous posts, but I didn't find a post that could help me solve the problem.
Thank you very much!

[tomfid]

Sounds like what you want is a logistic growth model. The model here https://vensim.com/vensim-video-library ... ith_Vensim has a variant of that near the 1hr mark, particularly if you make the product lifetime very long so that there's effectively no outflow from customers.

The general form is:

growth rate = max growth rate * (1-stock/ref stock) ~ fraction/time
stock = INTEG( growth, initial stock ) ~ stuff
growth = stock * growth rate ~ stuff/time

[Administrator]

There might be a molecule that does what you need (Tools->Molecules). There is a category titled "Close gap", maybe one of those?

[Nu_user]

Thank you @tomfid and @Administrator your advice really helped me.
The "smoothed quantity" molecule is very useful for my model! Also, the video library helps me in the understanding of the modeling process.