Ventana software support forum

Posted by Joel Rahn <jrahn@sympatico.ca> Richard Karash Richard Karash.com wrote: > Here is an example... It's the most remarkable beer game performance Are we still playing the Beer Game when the sectors are so flagrantly allowed to communicate with each other? R. Joel Rahn Posted by Joel Rahn <jra...

Posted by Joel Rahn <jrahn@sympatico.ca> As chairman of the 'Alternative Methodologies' thread at the last few conferences, I beg to differ with Messrs. Grösser and Toolan. Sure, a thread is not a workshop but it is an outlet for discussion about other approaches to modelling dynamic systems. To avo...

Posted by Joel Rahn <jrahn@sympatico.ca> Vensim (and probably other SD modelling systems) can do this by hot-linking Views (pages with text, diagrams, output) in a model or, with considerably more effort, by building a VenApp to present and run the model. Posted by Joel Rahn <jrahn@sympatico.ca> pos...

Posted by Joel Rahn <jrahn@sympatico.ca> Your interpretation is basically correct with a couple of added comments. 1. The rule of thumb for the delay times here is AT = AT1 + AT2 + AT3 2. The difference between the sequence of explicit first-order delays and an 'equivalent' third-order delay is in t...

Posted by Joel Rahn <jrahn@sympatico.ca> Almost simultaneous with my sending (SD5543), the suggested website ""for a different take on 'business process simulation' that is not discrete-event"" changed to the following: www.whatiftechnologies.com <http://www.whatiftechnologies.co...

Posted by Joel Rahn <jrahn@sympatico.ca> Wolstenholme's classification of archetypes includes both 'problem' and 'solution' versions. See: ""Towards the definition and use of a core set of archetypal structures in system dynamics"", E. F. Wolstenholme, SDR 19, 7-26 (2003) for com...

Posted by Joel Rahn <jrahn@sympatico.ca> dx/dt = x2 is a first-order dynamic system in the state (stock, level) variable x. The flow or rate is a second-order polynomial function of the state variable, because of the exponent. If the rate has more than one polynomial term, and only polynomial terms,...

Posted by Joel Rahn <jrahn@sympatico.ca> The most recent work is a paper from the Boston conference this year: Explaining Puzzling Dynamics: Comparing the Use of System Dynamics and Discrete-Event Simulation by John Morecroft and Stewart Robinson. For a different take on 'business process simulation...

Posted by Joel Rahn <jrahn@sympatico.ca> 'Order' is a more-or-less useful concept: interesting when talking about first or second order, occasionally when talking about third-order but hardly ever useful past that. Nevertheless, here are my two-cents' worth... The definition should read: ""...

Posted by Joel Rahn <jrahn@sympatico.ca> This situation sounds like the Fear & Greed archetype I presented at a poster session at the Boston conference. There is a very small model associated with the paper on the conference website. The paper itself was inspired by earlier work by Weaver, et al...

Posted by Joel Rahn <jrahn@sympatico.ca> Thanks for clarifying the underlying model and its use of revenue parameters to make the ServRatio dmensionless. The model described below uses the ratio of a stock, base, and a flow, sales, and it is the absolute rate of change of the stock that is involved,...

Posted by Joel Rahn <jrahn@sympatico.ca> I was perhaps a little flippant with my 'slope' comparisons; I am aware that there is a units problem. My comment was on a less-elevated plane and based on eyeballing graphs of behavior over time comparing only such features as the corresponding signs of slop...

Posted by Joel Rahn <jrahn@sympatico.ca> Jay's anecdote is interesting, pedagogically instructive and reveals more about the target audience (DEC managers) than it does about SD. Jay Forrest systems jayforrest.com wrote: >>Now, back to the model. It is not immediately obvious, but for this >>simple ...

Posted by Joel Rahn <jrahn@sympatico.ca> Jean-Jacques Laublé jean-jacques.lauble wanadoo.fr wrote: >>I do not see where I wrote that, I wrote exactly the contrary. I start with >>a simple model if I can, with no loop, and then choose to add a stock if >>necessary and so on. My comment was based on t...

Posted by Joel Rahn <jrahn@sympatico.ca> Foster's original questions were: >Can I have a complete Systems Dynamics Model without >feedback loops and still be able to demonstrate some >real world behavior? OR you always have to have >feedback loops in order to demonstrate behavior. These are not mutu...

Posted by Joel Rahn <jrahn@sympatico.ca> exp(a*t) is an exogenous function of time; it is equivalent to a Time Series. System Dynamics models may use time series inputs for various reasons but they are never part of the 'dynamic core' of the model. The proof: Given data time series inputs are usuall...

Posted by Joel Rahn <jrahn@sympatico.ca> [ Was Feedback and Behavior (SD5408) ] Integration over time is always accomplished by 'feeding back' the previous value of a stock in order to calculate its new value. In some dynamic modelling methods, this feedback is represented explicitly as a 'self-loop...

Posted by Joel Rahn <jrahn@sympatico.ca> Two books that contain several standard or 'classic' models that are often used as 'test-beds' and both are available from Pegasus: Study Notes In System Dynamics by Michael R. Goodman Managerial Applications of System Dynamics by Edward B. Roberts Goodman ha...

Posted by Joel Rahn <jrahn@sympatico.ca> The 'behavior' that SD models deal with is 'endogenously generated over an interval of time'. This requires feedback: change in a variable during a time interval is propagated through the dynamic structure (stock-and-flow, rates and levels) and modified in th...