Subject: help in pendulum model

Posted by Jay Forrester on 9/30/2008
In Reply To:help in pendulum model Posted by Steve Peterson on 9/30/2008

Message:

This characteristic of STELLA that prevents negative stocks and flows is one of the major reasons why many of us recommend using Vensim instead. If the STELLA designers feel they must mislead their users by implying that the real world operates without negative stocks and flows, the design should be set for full dynamic behavior as the default. The next best would be to have a global button that cancels all of the non-negative conditions in not only the existing variables in the model but also in any variables that are added later.


In K-12 education, the non-negative restraints should never be used. The students should think through the logic of how the real system is controlling flows and stocks so that they go deeper into the actual structure of the system with which they are working. I suspect that many in K-12 do not succeed in canceling the non-negative behavior in every stock and flow and as a result will often get misleading results.

Follow Ups:

help in pendulum model - Karim Chichakly 9/30/2008 
help in pendulum model - Jay Forrester 9/30/2008
help in pendulum model - Karim Chichakly 9/30/2008
help in pendulum model - Paul Newton 9/30/2008
help in pendulum model - Bill Braun 9/30/2008