Why is Vensim better than Stella?

[rkkalaga]

I have to teach modelling to high school students in India and have been evaluating both Stella and Vensim. The advantage I found with Vensim is that the PLE is Free to use and save the models for students, whereas Stella is not so. Are there any other distinct advantages of Vensim over Stella? It will be very helpful to get the needed inputs.

[Administrator]

You probably will not get many (if any) answers on this forum regarding Stella, as we are all Vensim users (some of us have experience using Stella, but not many).

It might be better to ask at the SD Society forum (http://www.systemdynamics.org/forum) or search through the archives of the SD mailing list (http://www.ventanasystems.co.uk/forum/v ... m.php?f=34).

[LAUJJL]

Hi
The biggest difference between Vensim and all the other SD software like Stella,I Think, Powersim etc.. is the Reality Check feature available in PLE version that has the main following advantages:
It permits to build a model from the needs of the client and verify that it respects them all along the building process which is rarely the case with other software.
The definition of the problem can be included in the model and is expressed in a rigorous mathematical way which is not the case with other software using other building methods.
You can address soft or hard problems much more easily than with other software.
The model built with reality checks have a high level of fiability and look much more valid to the end user.
You can build models not using reality checks like other software do, if you chose to do it.
See the chapter on Reality check in the User guide and the joined paper.
There is in the joined paper an inconsistency to my opinion. It proposes to build a minimum of 5 times as much RC equations than ordinary equations, which is too much. It calculates that minimum by multiplying all model equations by 5, which has no sense, because RC are built out of reality and not from the model, as it is explained in the paper itself. RC equations must be built from deep thinking about the reality that one wants to model and needs experience and a very different way of thinking that traditional deterministic and causal thinking.
Models using this method must be too built, starting from very small models and extended by very small added material and using and analyzing all the models produced intensively to understand them fully.
The method is unfortunately underused because it requires more work and especially more thinking and must be experienced, something that people are not ready to accept in present days.
Regards.
JJ

[tomfid]

Most of the big advantages in Vensim are in the advanced versions - it has better tools for model quallity control (including Reality Check), data handling, calibration, simultaneous equation solving and other advanced numerical methods.

Stella's strength is more in interface development and convenience of discrete event simulation.

The most conspicuous advantages even at the PLE level are on-the-fly simulation with Synthesim and causal tracing. These are important, because they make it easier to get a feel for a model and diagnose issues.

Tom

[rkkalaga]

Thank you all for your kind responses. Can Vensim be used for Business school case studies as efficiently as IThink?

[LAUJJL]

Business school cases are generally highly simplified and require gererally rather simple features that are shared by all SD software. Vensim being generally more powerful than I think, it will automatically be able to do anything that I think does. Vensim PLE is free for learning purposes and is sufficient for all business cases that never require sophisticated features. For example the mystrategy software si very oriented towards business cases and is less powerful than Vensim PLE version.
Regards.
JJ

[tomfid]

Vensim or Stella could certainly be used to create an equivalent representation of any b-school case. The advantage or disadvantage would be only a matter of the efficiency of using course material prepared for one platform on another. If you had a Stella model with an extensive interface, and you just wanted to distribute it for students to play with, it might not be worth the trouble to port it to Vensim. But if you're having students build models from scratch, there wouldn't be much of a barrier to switching.