Ventana software support forum

Hello,
I'm working on a simple model to calculate end of life vehicles based on sales. When I used other SD software, I was able to have subscripts as number, and made use of time to spread out the sales by year. However, because Vensim subscripts only accept text, I have to work around by entering a function for each subscript, which is time consuming. Another issue is that I also have to track vehicle age by using a stock, instead of having age as a subscript like the other software.

Is there a better way to model this other than my work around approach? Any feedback is highly appreciated. Thank you!

Ruby

There is a sample model that ships with Vensim that should help.
On the Mac, you will find it at
/Users/Shared/Vensim/Help/HTML/Models/Sample/EXTRA/TUBS.MDL

on Windows, it's something like
c:\users\public\Vensim\Help\HTML\Models\Sample\EXTRA/TUBS.MDL

This model is what I always start with if I'm looking to capture the ageing process. Tubs is a set of bathtubs that fill sequentially, but it's easy to extend this to an age structure and move everything from one "age" to another after a fixed period of time.

There are also a lot of hits on Google if you search for cohort and Vensim.

PS. You might want to look at Ventity as well which handles this kind of thing much easier.

Thank you, Admin! I've been thinking about Ventity as well. One general question: once switched to Ventity, is there a reason to come back to Vensim? In other words, is Ventity an improvised version of Vensim? Will Ventana plan on supporting both or eventually will only support Ventity? Thanks!

Both will be supported for the foreseeable future.

They have different strengths. If you have data with a sparse or ad hoc key structure, or you need dynamic creation/deletion of entities, Ventity makes a lot of sense. But Vensim has some unique capabilities as well, including richer optimization options, web publishing, and simultaneous equation solving.