Ventana software support forum

X-Mozilla-Status: 8011 X-Mozilla-Status2: 00000000 X-UIDL: 10440-938505322 Status: O X-Status: > "Try linking the inflow > directly to the outflow > (bypassing the stock) ... > Perhaps Im missing something here, but > isnt it a violation of the fundamental > concepts of the System Dynamics appr...

Part of the answer to this question depends on the purpose of the model (as always). Creating a structure that accurately represents the distribution of maturing shrimp over their three months in the lagoon may be a waste of time if the pulse passes into a large stock of oceangoing shrimp with a lon...

Jack Homers Burnout model is included in the sample models distributed with Vensim. You can also download a copy from my model library ( http://home.earthlink.net/~tomfid ); it can be run with Vensim PLE. Tom **************************************************** Thomas Fiddaman, Ph.D. Ventana Systems...

Jay Forrest wrote: >It seems to me that Bruce is disconnecting logic or structure from output. >I must propose that the accuracy of the output need have no relationship to >the accuracy of the underlying structure and that the insights gained from >a poorly designed but brilliantly calibrated (or co...

I think Bryans referring to Maxwells third and fourth equations, which relate electric and magnetic fields to the rates of change of magnetic or electric fluxes. This shows up most often when talking about inductors, which appear in simple circuit equations with a derivative of current, e.g. V = i*R...

"Diffusion of a not known methodology in an environment" sounded interesting, though I couldnt exactly pin down the goal of the work. Nevertheless, Im attaching some references I dug up in the past, mostly motivated by my research on diffusion (or other positive feedback processes) of ener...

Friends, Ive just updated my SD web links page, at: http://home.earthlink.net/~tomfid/ Many new links have been added, particularly to sites on advanced methods. Ive also added two new models to my model library, on stochastic inventory management and learning curve strategy. Ill be further updating...

Christian Kampmans dissertation, "Feedback Complexity and Market Adjustment: An Experimental Approach" (MIT, 1992), contains some examples of hill-climbing behavior rules (setting price and quantity for profit maximization). Its a bit thick, but I consider it a must-read for advanced SD pr...

For a nice complement to the SD interpretation of amplification of disturbances up a supply chain, see Steve Graves article in the first issue of the new M&SOM journal: Stephen C. Graves, "A Single-Item Inventory Model for a Nonstationary Demand Process." Manufacturing & Service Op...

>Should we use 0-off, 1=on to indicate an on-off switch in a thermostat? Thats what I would do, because of the binary switch analogy. >To what extent does this require incorporating DT into the equation? You still need DT (TIME STEP in Vensim) on the RHS of an equation: Switch State = INTEG( Switch ...

Guenther Ossimitz wrote (edited for brevity): >4) Wayne Wakelands binary "furnace on-off 0-1 stock" is >really a great idea - if you want such a thing at all in a >SD - model. Of course a flow of 1/DT is the only possiblity >to maintain such a stock. however, it is easy to prevent >the 1/D...

Its right to note that many SD practitioners dont think kindly of optimization. However, this should be viewed as a rejection of optimization as a behavioral assumption, rather than optimization as a tool. Much of the criticism of Senge, Forrester, et al. has been directed at economic models that as...

A copy of Nathan Forresters dissertation model, mentioned by Mike Radzicki, can be found in my model library at: http://home.earthlink.net/~tomfid/models/models.html Look for the listing: Dynamic Synthesis of Macroeconomic Theory Provided by Nathan Forrester See: Forrester, N.B. (1982) A Dynamic Syn...

A classic work here is Forresters _Industrial_Dynamics_ (1961). Though it doesnt directly refer to JIT, MRP, etc., its a must-read. The book is available from Productivity Press, and one of its models (Chapter 15) is available on my web site at: http://home.earthlink.net/~tomfid/models/models.html S...

Encoding a production process in an RCA is an extremely interesting idea. Cellular automata arent really my bag, but Ive only seen examples from physical or biological sciences where there is an obvious spatial interpretation. Im interested to hear more about the production process and how it could ...

>of variable delays can be easily simulated in Stella/iThink by using >conveyers as the delay element and using some function of >NORMAL(mean,sd) to vary transit time (or any other distribution for >that matter). Im not sure a conveyor with a fixed transit time quite captures the spirit of David Pet...

David Petersons comments are right on. Here are a few supplemental thoughts: One of Forresters experiments with delay order is in Appendix H of Industrial Dynamics (available from Productivity Press, and a must-read). It compares the effect of 1st-, 3rd-, and infinite-order (pipeline) delays in the ...

>We have recently been informed in these discussions (again) about several >biological models developed by SD students (diabetes, menstrual cycle), and >I applaud this work. But I am really waiting (and pushing) for the time >when these models are developed by the biomedical researchers themselves, ...

There are many SD models of economic problems in which agents solve allocation problems by local hill-climbing. For an example, see John Stermans model on the use of aggregate production functions in the Model Library of my web site (link below). The model illustrates a behavioral interpretation of ...

You should definitely get in touch with Elizabeth Keating at the MIT Sloan School, who has done a lot of conceptualization work around this issue (focusing on the Grameen Bank). I dont have a current e-mail address handy, but you should be able to reach her through MITs directories. - Tom **********...

For help desk call volumes, Rogelio Olivas MIT PhD thesis on service qua= lity may be of interest: Oliva, R. (1996). A Dynamic Theory of Service Delivery: Implications for Managing Service Quality. Sloan School of Management. Cambridge, MA, MIT. In software development Tarek Abdel-Hamid has done a l...

>A prof of meteoroly at MIT [name escapes me, but I have the refer >at home] stated that"science does not predict climate". His name is Richard Lindzen. I dont have any recent citations, but the following is a start: Lindzen, R. S. (1990). =93Some Coolness Concerning= Global Warming.=94 Bu...

>Since solving the chemical equations is effectively solving a system of linear >equations I presume that there must also be a means of solving (or simulating) >linear and non-linear systems of equations using SD. Im having a hard time dusting off my chemistry, especially because my chemistry text i...

Check the links under Spatially Disaggregated Models on my web pages. Theres been some interesting work at Cranfield in the UK (Peter Allens group) and at U Maryland (Bob Costanzas group). One of the Maryland sites includes links to a software package theyve developed that does what youre after, I t...

Friends, Ive recently finished an update to my web site, including the following areas that I hope will be of interest to you: - about 100 links to sites in system dynamics and other simulation and mathematical modeling disciplines - about 100 links to climate change, energy, economics, and environm...