Subject: DYNAMO

Posted by George Richardson on 12/16/2009
In Reply To:DYNAMO Posted by George Richardson on 12/15/2009

Message:

One more thought about DYNAMO:

It is often a very enlightening exercise to translate a model from one modeling environment to another, e.g., to translate World2 (Forrester's World Dynamics model) from DYNAMO into STELLA. The best way to proceed is to draw in STELLA (or Vensim or PowerSim) the diagram of, say, World2, and then formulate the equations to match the DYNAMO structure.

Of course, there already exist versions of World2 in STELLA (and Vensim and PowerSim. etc.). But the translation exercise still has a lot of merit:

- You start with a model of known behavior and try to recreate it. Inevitably, somewhere among the 50+ equations, you make a minor (or major) mistake, and find that the model does not "reproduce its reference modes," that is, doesn't behave like the original. So you have to work with it to find out why. Very enlightening exercise in understanding model structure and behavior.

- You get some greater understanding and appreciation for the good things that STELLA (and Vensim and PowerSim) is doing for you. The treatment of graphical functions, for example, is much more intuitive.

- You focus deeply (deeply!) on the model being translated. You'll probably know more about World2 when you finish than you ever would know just experimenting with the model. And your understanding will come more quickly.

The downside, of course, is you have to know enough about DYNAMO syntax to do the translation. And that syntax is nothing you need to know for your future work. So it's an investment with a small immediate payoff but not much long-run benefit. (I used to assign such translation exercises from the early urban models, but I've stopped the practice. My students found it extremely instructive, but learning enough about DYNAMO to do it was a drag.)

...GPR

Follow Ups:

DYNAMO - Bill Braun 12/16/2009 
DYNAMO - Leonard A Malczynski 12/16/2009 
DYNAMO - Alex Leus 12/16/2009 
DYNAMO - World3 in STELLA - Lees N. Stuntz 12/16/2009