Discrete Processes Stella Vs Vensim

[karankhosla]

Recently, there have been many posts about discrete functions and also references to the numerous books/examples on management written using Stella's discrete processes.

A few years ago, I created a Vensim model (Based on the "grocery model" Chapter 4 in Bruce Hannon's: Modeling Dynamic Economic Systems) to mimic the output of a simple Stella process using all three discrete processes [queues, conveyors, ovens - typically used in the books]. However, the outputs of the same process did not quite match up in either software; since Vensim is our software of choice, I modified the Vensim model by adding certain structures to get the outputs to match.

I'm not sure this will be of use to anyone (I don't use these functions much), or if it even makes much sense as yet; but it is extremely interesting to see how these discrete functions differ in output under certain conditions in both software packages.

I tried very hard to understand and explain what Stella is doing (and why?); please see comments in the equations. Unfortunately detailed documentation on these functions is not available for Stella.

I have attached the same model in both formats i.e, Stella and Vensim.

My Best Wishes,

Karan

[Edited on 9-21-2010 by karankhosla]

[Edited on 9-21-2010 by karankhosla]