Ventana software support forum

A fuzzy relation between two variables can be de-fuzzified to make a LOOKUP function Vensim (formerly TABLE function in DYNAMO) and a LOOKUP function can represent a fuzzy relation between two variables. The whole argument rests on a representation theorem for fuzzy relations that says, essentially,...

In reply to George Simpson's REPLY: A large model is anything but transparent. I was not thinking of using a neural network to replace an SD model. I just thought that the parameters of the network model might say something about where the important loops are i.e. the loops that dominate a certain b...

Perhaps the question we should be asking ourselves on this list is whether a neural network model of an SD model could tell us something about the important causes of the model's behaviour, and if so, is it more efficient to use a neural network instead of the dominant-loop or dominant-mode approach...

Wolfram's approach exploits the properties of cellular automata first made famous (early 70s) by Conway's Game of Life in which local rules for creating/destroying cells give rise to intriguing patterns on a monitor when the cells are represented as pixels that are lit or dark according to the state...

At a presentation of the SD approach to resource management (human,
equipment, financial resources), someone asked how SD compares with
System Design Engineering. Any enlightenment from this list would be
welcome. Thanks

Joel Rahn
jrahn@sympatico.ca

I hesitate to stir up this sort of hornet's nest but field theories (electro-magnetic, acoustic,...) do not use material stocks and flows and they can represent such phenomena as the Doppler effect. However quantized versions (photons, phonons,...) use flows and densities (i.e. numbers per unit volu...

Gord Kubanek (and I to a lesser extent) is looking at Anylogic as an
alternative to SD for HR problems. Should have something to say in about
a month.
Joel Rahn
jrahn@sympatico.ca

Jim Hines wrote: >J.J. Laubles is extremely clear (and concise!) in providing the principle >that must guide much (but maybe not all?) statistical testing: If you can >prove A implies B with only a 5% chance of error. And, if you can prove that >B is not true, then youve proved that A is not true wi...

John Sterman wrote: > My good friend Jim Hines "question[s] whether statistical estimates > have any rational claim on our attention other than widespread use and > anecdotal evidence of usefulness." Jim wants rigorous demonstrations > of the value of statistical reasoning and estimation m...

Jim Hines wrote: >Ray says " Lets make sure we are talking about the same thing. " > >So just to be clear, were talking about two separate dimensions of a >model: A time dimension and an event dimension. Time can be either >discrete or continuous. Events can either be discrete or [insert a...

Now that I know what we are talking about, and inspired by Jims diagrams, I suggested that "repeated event" describes Jims "extended event" when it occurs in discrete time and "interval event" describes a Hinesian "extended event" in continuous time. Sorry it ...

You are dealing with confidence intervals. A good simulation text like Law & Kelton will give you an answer with the usual caveats about using such intervals. A quick answer is: no. of replications = Variance* (z(alpha/2)/half-interval of confidence)^2 where: z(alpha/2) is the appropriate Normal...

This seems to be a model about recycling. If so, the classic reference is Jorgen Randers chapter in Dynamics of Growth in a Finite World. Another source of inspiration may be an issue of Interfaces published by The ORMS Society (or INFORMS as it is now) in 2001 I believe. There was an article about ...

The classic reference, as many will no doubt reply, is Jim Lyneis book: Lyneis, J. M., Corporate Planning and Policy Design, MIT Press, 1980. Check with Pegasus Communications for current availability. Jims book does not deal in _great_ detail with the engineering/operations sector but it has the es...

A short answer to Daniel Janoschs question is: The SARS epidemic is worthy of caution but not yet panic. Media hysteria has not been abated by the way public health authorities have handled the ever-changing information about the disease and its spread. From my vantage point here in Quebec City, I w...