Search found 55 matches
- Sun Jun 18, 2000 11:01 am
- Forum: SD Mailing List Archive
- Topic: linking flow to flow directly?
- Replies: 9
- Views: 36016
linking flow to flow directly?
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...
- Thu Jun 15, 2000 3:50 pm
- Forum: SD Mailing List Archive
- Topic: Delaying shrimp migrations
- Replies: 4
- Views: 4367
Delaying shrimp migrations
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...
- Wed Apr 05, 2000 2:40 pm
- Forum: SD Mailing List Archive
- Topic: Levels in Abstract Models
- Replies: 4
- Views: 3857
Levels in Abstract Models
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...
- Thu Mar 16, 2000 3:02 pm
- Forum: SD Mailing List Archive
- Topic: System Dynamics: Art, Science or Profession
- Replies: 19
- Views: 13209
System Dynamics: Art, Science or Profession
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...
- Thu Feb 24, 2000 1:29 pm
- Forum: SD Mailing List Archive
- Topic: Causal loop and Stock and Flow Diagramming
- Replies: 8
- Views: 7711
Causal loop and Stock and Flow Diagramming
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...
- Thu Jan 27, 2000 11:08 am
- Forum: SD Mailing List Archive
- Topic: New Methodology diffusion
- Replies: 5
- Views: 5197
New Methodology diffusion
"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...
- Fri Jan 14, 2000 3:44 pm
- Forum: SD Mailing List Archive
- Topic: Web Links Update
- Replies: 0
- Views: 2187
Web Links Update
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...
- Fri Dec 10, 1999 11:49 am
- Forum: SD Mailing List Archive
- Topic: self optimization
- Replies: 4
- Views: 12908
self optimization
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...
- Tue Nov 09, 1999 11:50 am
- Forum: SD Mailing List Archive
- Topic: bullwhip effect on the supply chain.
- Replies: 5
- Views: 14858
bullwhip effect on the supply chain.
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...
- Tue Nov 09, 1999 11:45 am
- Forum: SD Mailing List Archive
- Topic: DT and furnace/thermostat models
- Replies: 4
- Views: 14657
DT and furnace/thermostat models
>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 ...
- Sun Oct 31, 1999 12:41 pm
- Forum: SD Mailing List Archive
- Topic: Negative Levels, furnaces
- Replies: 0
- Views: 9331
Negative Levels, furnaces
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...
- Tue Dec 01, 1998 10:56 am
- Forum: SD Mailing List Archive
- Topic: Optimization and SD
- Replies: 5
- Views: 4388
Optimization and SD
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...
- Mon Nov 23, 1998 10:29 am
- Forum: SD Mailing List Archive
- Topic: IS-LM model or a like macroeconomic models
- Replies: 4
- Views: 11414
IS-LM model or a like macroeconomic models
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...
- Fri Nov 13, 1998 1:33 pm
- Forum: SD Mailing List Archive
- Topic: Modelling Manufacturing Systems
- Replies: 2
- Views: 10445
Modelling Manufacturing Systems
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...
- Fri Nov 13, 1998 9:51 am
- Forum: SD Mailing List Archive
- Topic: More on reverse modeling
- Replies: 1
- Views: 8985
More on reverse modeling
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 ...
- Fri Oct 23, 1998 10:34 pm
- Forum: SD Mailing List Archive
- Topic: Normal distribution
- Replies: 7
- Views: 15650
Normal distribution
>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...
- Thu Oct 15, 1998 11:40 am
- Forum: SD Mailing List Archive
- Topic: Normal distribution
- Replies: 7
- Views: 15650
Normal distribution
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 ...
- Thu Oct 08, 1998 1:16 pm
- Forum: SD Mailing List Archive
- Topic: Validity of Models
- Replies: 4
- Views: 7016
Validity of Models
>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, ...
- Mon Sep 28, 1998 1:14 pm
- Forum: SD Mailing List Archive
- Topic: Economic modelling and SA
- Replies: 2
- Views: 3824
Economic modelling and SA
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 ...
- Mon Sep 28, 1998 12:55 pm
- Forum: SD Mailing List Archive
- Topic: Modelling revolving loan funds
- Replies: 1
- Views: 2829
Modelling revolving loan funds
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 **********...
- Mon Jul 27, 1998 10:38 am
- Forum: SD Mailing List Archive
- Topic: Software Development and Support Models
- Replies: 3
- Views: 3522
Software Development and Support Models
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...
- Thu Jul 16, 1998 2:01 pm
- Forum: SD Mailing List Archive
- Topic: Energy 2020
- Replies: 11
- Views: 30172
Energy 2020
>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...
- Thu Jun 04, 1998 11:46 am
- Forum: SD Mailing List Archive
- Topic: Modelling chemical reactins for chemical formulae
- Replies: 7
- Views: 5819
Modelling chemical reactins for chemical formulae
>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...
- Wed May 20, 1998 6:08 pm
- Forum: SD Mailing List Archive
- Topic: 2-D SD models and Linking with GIS
- Replies: 0
- Views: 1962
2-D SD models and Linking with GIS
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...
- Wed Apr 15, 1998 9:47 am
- Forum: SD Mailing List Archive
- Topic: Updated Web Links and Model Library
- Replies: 0
- Views: 1426
Updated Web Links and Model Library
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...