Ventana software support forum

Woncheol Kwak wonders about whether he should use system dynamics: >The entities in my customers business process seem to be too complex to >me to model with System Dynamics and I dont have much time to >thoroughly examine the potentials of SD. Woncheol, The good news is that the process is not too ...

Im delighted to announce some promotions and changes in the MIT System Dynamics Group. Nelson Repenning has been promoted from assistant to associate professor, and has been named J. Spencer Standish Career Development Professor. Career Development chairs recognize and support outstanding junior fac...

> In medicine, we often hear that cells respond to the rate >of change of some sensory input, which would appear to contradict Organisms, organizations (e.g. revenues), and mechanisms (e.g. speedometer) sense the rate of change via an average change over some **finite** time interval. That is they s...

We certainly are saying a lot about a little. But ... In order: Goeff Coyles definition of "recursion" is perfect. But it just raises another question: Whats the word for a definition that ***demonstrates*** its meaning. For those who still understand analogies (a much beloved, but now dec...

My recent response to Geoff, Neal and Bob contains a typo. A greater-than sign should appear in my suggested improvement to Bob’s equation, rather than a less-than. The correct equation is outflow = if (stock > normally indicated outflow*dt) then (normally indicated outflow) else (0) Jim From: "...

Geoff Coyle sparks interesting questions about widgets and dt. First is the question of where the word "widget" comes from. According to the American Heritage Dictionary, the word "widget" is "perhaps [an] alteration of gadget". According to the same respected source th...

Nail Palfreyman suggests that object-oriented modeling and SD have a lot to learn from each other. My guess at this point is that an object oriented modeling approach might work well when you are building a model of a type you are already quite familiar with. I speak a little from experience: I buil...

Raymond, Its very nice to hear from someone as experienced as you. Is your experience specifically with system dynamics models or with other kinds of models? In reply to your points: Of the three benefits you mention, the only one I wonder about as I try to imagine what youre doing is the second one...

Andy, Very interesting! Starting with a demo model that has "mini" versions of the sectors all tied together with the major feedback loops is neat. I can see how that would work. How do you coordinate the sectors. For example, as sectors get built-up, do you update (what was) the "min...

Martin, Its good that you are using the "standard method" for each of your sectors. But, Im concerned for you about developing the model by sectors. Dividing a model into sectors is a common strategy in SD, but not one that always (usually?) works. The problem is that when the modeler hook...

Martin Busse asks about the National Model -- its current status and who has worked on it. Jay Forrester is continuing work on the model. Many people have worked on the model including Bob Eberlein (this lists moderator), Alan Graham, Gil Lowe, John Morecroft, Nat Mass, Nathan Forrester, Peter Senge...

Raymond, I was curious about one thing you said: Im not sure that all physical processes are discrete in nature -- even at the sub-atomic level. At the sub-atomic level some people visualize an electron as forming a cloud, dont they? And a photon can be considered (and "physically" viewed)...

Bill Braun asks >Can forecasts of the future be dynamically modeled, with information from >stocks (that represent a future state) feeding back into current decisions? The answer is generally "no" in a **model** because using knowledge of a future state in current decisions will usually af...

Take a look at Software Project Dynamics: An Integrated Approach by Tarek Abdel-Hemid, Stuart E. Madnick. 1991. Prentice Hall. (Available at Amazon). The book develops a project model of a software project. The model is adequate. But, the insights that the authors get from the model are first rate. ...

Gebhard asks: What kind of knowledge and experience exists in integrating qualitative data [into an SD model]... How do you avoid black box correlations in these cases? Theres lots of experience out there. People like Jim Lyneis, David Peterson, Alan Graham, Ken Cooper, George Richardson, David Ande...

Nail mentions a feeling that his comments have not always matched what was expected and feeling that there is something exclusionary about the list. A couple of people have already mentioned the PC view that no one should be feel excluded. (Note: Just because its politically correct doesnt mean its ...

As Geoff Coyle says, we owe Bob Eberlein many, many thanks for this discussion list. To correct any misunderstanding, The System Dynamics Society has never had a role in the list. Any confusion probably results from the fact that many members of the Society are valuable contributors to this list -- ...

Were adding Environmental Dynamics to MITs distance course offerings. The course is taught by Forrester Award winning author Andy Ford. MITs distance program now offers seven for-credit courses in system dynamics via the web. Were currently accepting applications for the term that starts in late Feb...

The System Dynamics Society publishes the "System Dynamics Newsletter" which has a section on New Books by Members. If you are a member and have recently authored a book please send your name, the year of publication, the title of the book, the publisher and address, ISBN and website if av...

A slight clarification of Bill Harris statement about Vensims equations and views. Vensims views and equations are **always** synchronized. A new variable created in the equation editor will "magically" appear on any view that has equations that directly use the new variable. (The variable...

Bill Braun asks if the Urban Dynamics attractiveness formulation is still considered useful. The answer is yes. This formulation (modified just a bit) represents an SD "molecule" or standard formulation that everyone in the field should have at their finger tips. (A molecule is a tried and...

Rohita Singh gives us some additional contrasts between SD and discrete event simulation. I have one small clarification, though on her point 3, which deals with discrete vs. continuous. The contrast here is not between discrete vs. continuous time, but rather between whether events happen at a sing...

I think the difference between system dynamics folks and discrete event folks is the following: 1) The modeling **techniques** used by the two different groups are usually different at two levels: (1) The modelers way of representing systems is different and (2) the underlying simulators algorithms ...

Most folks simply say that the order of a system is the number of stocks in
it. I think this is really fine, although its true that sometimes you can
find an equivalent system with fewer stocks.

Jim
From: "Jim Hines" <jhines@MIT.EDU>

We are now accepting applications for the Fall term for MITs Advanced Study Program in System Dynamcis. This program is a series of web-based courses in system dynamics. There are now six offerings (three full semester courses and three half-semester advanced topics). Each course and topic is offere...