Ventana software support forum

Time itself may be not be a stock, but there are many resources that are not stocks that need to be allocated (electricity, for example) The stock verses flow characteristic of the resource is not relevant. The control of its use is. By definition, the control is part of a feedback loop. By definiti...

It may ultimately be shown that David Peterson is correct in his perspectives on RUM allocation, but I do not believe the objections he raised bear out. I still contend that Alloc_p is an ALGORITHM to allocate resources. As taken from the VENSIM c-code and Woods own work, its only departure from a &...

George Richardson wanted to use: MIN( Tj, Wj*Tj/sum(Wi*Ti) * Total time available ) to get rid of the "over or under" allocation problems. Note that: Sum(Wj*Tj/sum(Wi*Ti)) is unity and, therefore, the minimum function is not needed. There could, however, be a problem with the simple weight...

Guenther Ossimitz felt that an inter-personal argument had no intervening levels. As SD theory claims, it does. Many of us who must attempt to solve client problems, live in an adversarial environment. Whatever we recommend will change the system conditions and affect some member of that system. The...

Relative to Jim Hines comment about the force and counter-force on a table. The logic is just the force law and it is described (even in conventional physics) as an auxiliary equation -- no loop. If the force does work, there is integration (momentum or distance or velocity depending on your interes...

I think we are letting cross-paradigm semantics grossly misinterpret the critical, key point Khalid is trying to make. All good SD models contain causal circular flows. We call these feedback loops. These feedbacks loop are NEVER defined in terms of simultaneity - remember good ol rates and levels b...

Elaine, I think we have "talked" before. We use HYPERSENS to determine the value= of data. (You can look in the SD Bibliography under Andy Ford, Jeff Amlin, a= nd myself to find references to HYPERSENS use in the electric utility industry. Andy also notes it in the appendix of his new book...

Pete Warrian was interested in the use of SD to look at the impacts of electric deregulation on industrial users. ENERGY 2020 has been used to look at deregulation in all 50 states and all the Canadian provinces. It simulates industrial users by end-use for all fuels at the 2-digit SIC level. We oft...

Snow is really important to Eskimos. They have many names to describe the nuances of different conditions of snow because it is important to their survival (e.g. how fast can they move on the snow, how fast is the temperature falling, etc.). As they are "snow people," we are "systems ...

This note seems to indicate a different view of the word "systems." It is true these noted individuals did grab a system with large boundaries (although Einstein only assumed one simple steady-state universe rather than the multiple dynamic ones we now "know."). But the boundary ...

Eduardo Giordanelli and others are concerned about whether system dynamics is really a good forecasting tool in the absolute sense. I think most people would agree that SD and all other methodologies CANNOT produce "accurate" forecasts. As someone noted, the future only occurs in the futur...

Anthony Gil is concerned about the use of the forecast. This may be the most important issue surrounding forecasting models. Most everyone who is unfamiliar with SD and feedback thinks a forecast is a objective item; "just give me the truth." How the forecast is to be used is what determin...

Anthony Gil was worried about the UK Treasury models. First, there is chaos in real-world commodity systems (my personal, only partially substantiated, view) that limits the ability to "hit right on, "but, second, in the UK, the models of both David Hendry (Oxford) and Terry Barker (Cambri...

John Swanson wanted to know about forecasting with SD. We have hit this topic on the server before but ..... Although forecasting is far from the best use of SD, it would appear that it can be as, if not more, accurate (valid) than any alternative. The biggest problem is the inclusion of additional ...

Gopt, SD is used by Environment Canada to address climate change issues (most recently for NAPCC.) NRCan has used SD since 1990 for energy planning. BC Hydro uses it for deregulation analysis. BC Gas has used it for forecasting, and Saskatchewan Energy and Mines uses it for Energy Policy. CERI (Cana...

Khalid Saeed writes: "Wouldnt an attempt to understand the slack problem and the dysfunctional feedback structure be more useful. Wouldnt this be better attempted without noise adding confusion to the analysis?" I appreciate and agree fully with Khalids comments, but if we were really smar...

Bill Harris said: > I heard Peter Senge talk a couple of years >ago, and he was saying that their (SoL?) data didnt indicate a strong >correlation between top management buy-in and survivability of change. All those involved with Learning Organizations (LO) in SD have done SD a great service. Becaus...

I would think risk management would be an excellent use for the Latin-Hypercube (LH) tools in Vensim. You can add the noise to the system and add the Black-Scholes equations as desired. You can the use the LH to make the uncertainty for the B-S equations and solve for the portfolio set needed (using...

The consulting industry mantra is "sell at the top." Often SD does not. If the problem is important enough (lots of negative $ on the line for the company) and tough enough (the company has already unsuccessfully gone through the "other" methodologies looking for the solution), t...

I think the climate change discussions have a deeper relevance to the SD practitioners. While I agree with Tom Fiddamans concerns (and greatly respect his work on the subject), it misses the point that no one can cla= im he/she has THE unique understanding of the CO2 cycle. We do not really understa...

I was gone over the US holiday and just saw got back to find SD 1524 = note on asymptotic CO2 levels. I also saw John Stermans SD 1528 = response and am afraid I agree with John. =20 I must also confess here about our work. As I looked at the CO2 data, I = could find no compelling evidence for or ag...

We have some "hype" and other documentation that I can send to anyone who requests it. Our Web page is in really bad shape until we can "come up for air." Therefore, it is NOT a good place to look for now. ... I agree that the CGE models are not all bad and they can pick up many ...

Hi Dean, I worked with Abha Bhargava on her (now old) version of the SEM model. Jeff Amlin and I are the primary co-authors of the last decades set of incarnations, although a large number of system dynamicists who went through Dartmouth College and MIT in the late 1970s and early 1980s get to take ...

In reply to Bill Harris: > Now the real answer to why the model made "good forecasts" is that once you > have a system that counter-responds to any changes no mater how dramatic, > ^^^^^^^^^^^^^^^^ > Can you explain what you mean here a bit more? Do you mean that it By this I mean one of t...

In response to John Noble; Our group, for right of for wrong, has used SD extensively for pin-point forecasting in the energy industry for 20 years. We spend a great deal of time going head to head with econometric forecasts and their entrenched staffs. So far we have always "won" against ...