Ventana software support forum

I appreciated Raymond Josephs response to my question whether statistical estimates have any rational claim on our attention other than widespread use and anecdotal evidence of usefulness. I interpret his answer as being "no", which may seem odd (to him especially) because he wrote "y...

I think there may be an impression brewing that (1) everyone agrees with what Jay said about validation and (2) Jay said validation isnt possible. This is not right on either count. 1) Jay never said that validation isnt possible. He said that validation is a process of increasing confidence in a mo...

Kim asks whether you can validate a model using multiple regression techniques on the equations of rates and auxiliaries with the stocks as independent variables. (He explains why he believes the technique would fail using the stocks as dependent variables). When Kim says "validate" I thin...

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 word here that means a...

Bill Braun asks me to choose a term for what I was calling "continuous event", a term to which Yaman Barlas objected. I think the term should be chosen by someone who cares. Id be happy though to throw out a few terms that I think would do nicely (and which I think Yaman would also be happ...

6 Yaman Barlas writes: >I would either call [a "continuous event"] a series of >discrete events (in the discrete-time case) or something like >a process in the continuous-time. The important thing to me is to have a **single** name that contrasts with the term "discrete event". C...

Bill clarifies terminology and asks for more precision from me on what challenge I wanted George Simpson to issue. Precision is actually what Im hoping will come out of George Simpsons challenge and the resulting responses. I really am intrigued by Georges original statement, really dont know exactl...

Im intrigued by George Simpsons statement "The essential difference [between the discrete event approach and the way SDers usually model] is that what is flowing in discrete simulation carries information, which can affect the flow itself." George, how about laying down a challenge to the ...

Our (Paulo Goncalves, Charlie Lerpattarapongs, and my) work suggests that pull components in a supply chain add significantly to stability. The reason is that a pull component creates a very fast negative feedback loop. (Paulos thesis is the best place to see the work --- hes provided a citation in ...

I believe that Khalid Saeed will follow with a more official sounding announcement -- but allow me to squeak in here with a news flash: The distance program in system dynamics has a new home -- WPI. All the profs and instructors in the distance program (currently seven courses offered world wide) ar...

Isnt a traffic Jam basically an inventory oscillator with each driver
trying to maintain an "inventory" of space between himself and the car
in front? Thats what John Sterman told me.

Jim
jhines@mit.edu

Weve had a number of posting from folks who are doing SD in their companies. The latest from John Ewaldt and A. Ilker Soydan in two companies I had no idea were interested in SD. The sad thing is that graduating Students are always asking what companies MIGHT provide an opportunity for them to at le...

A. Ilker Soydan wrote "...the firm [Seimens] started launching SD to itself and started speaking in terms of SD." Question to A. Ilker: Would you describe the process underway at your company to launch SD and where Seimens is now in the process? E.g. did it start within an internal consult...

No one has ever gone wrong following Georges advice, and many many people have become better people for having embraced Georges views. Unfortunately, its easy to misinterpret Georges recent injunction -- Im writing because a respected friend did just that. Fortunately, I have an almost mystical bond...

An addendum to Jim Thompsons note: "When the model we create does simulate reference mode behavior, we improve the likelihood of achieving that objective [of understanding reference mode behavior]." And even when we create a model that does NOT simulate reference mode behavior, we improve ...

Only one quibble with Bill Brauns suggestion of what we call what. A problem focus is really just the problem that the modeler is focused on. Observability, measureability, general recognition, importance to the organization -- none of these things are necessary or sufficient. A student could have a...

I mentioned earlier I didnt think incorporating learning in a model would jeopardize a models problem focus. That struck Bill Braun as odd enough to wonder if I was actually referring to models that really learn ("and thus change"). I think I was referring to that kind of model, but its to...

If I understood Bill Braun email, he asked if a model that learns can remain focussed on the original problem. The issue of problem focus is separate from the issue of representing learning within a model. Focusing on a problem is "just" a strategy for creating a useful model. The particul...

Weve been working for several years modeling social learning in organizations. The specific question weve been asking is how can you structure an organization so that managers tend to learn (and create) better policies (in the SD sense). This work combines system dynamics with agent-based modeling a...

A couple of people have written to ask how to get Alans and Nathans theses. Bill Harris is probably fielding similar queries. Heres the scoop: The thesis are available from the M.I.T. Libraries Theses Collection. The titles and dates are A dynamic synthesis of basic macroeconomic theory : implicatio...

Bill Harris is right about the usefulness of Alan Grahams Ph.D. dissertation for understanding the relationship between structure and behavior. If you havent read it, you have something to look forward to: Put it at the top of your list of what to read next. Another wonderful dissertation about &quo...

It looks like the time has come for Magne Myrtveits 1995 proposal at the Tokyo Conference for a interchange language. Unlike then, I think the society now would probably sponsor such an effort. I suggest we have an organizing meeting at the New York conference this summer. Everyone with an interest ...

(1) Jim Thompsons most important question is whether the users can offer any kind of incentive to vendors for incorporating the ability to export and import SMILE files. Nothing very good comes to my mind, which is why its such a dandy of a question. Just to illustrate how nothing very good is comin...

There would be many benefits to a simulation model interchange language (smile). Just to list some, starting with the one that Carolus names: A SMILE would ... 1. Make it easier for colleagues (or potential colleagues) to exchange views best expressed as models (where the exchange would preserve bot...

Timothy Fong asks an interesting question about modeling when it you dont have enough information to answer a clients specific question -- e.g. how much marketing dollars to spend. The first question -- how much to spend -- probably cant be answered as precisely as the client wants, because you dont...