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Our newest member :	Viet Cuong Do
Most users ever online was 133 on Wed Jul 07, 2010 1:17 pm

Re: XMILE

11680 — 2012-02-01T15:32:20-05:00

Thanks for your valuable comments, Jean-Jacques. I share your frustrations; you are asking the right questions; and I agree that making a simple SD markup language is easily achievable and desirable.

I should make it clear that I have no particular inclination towards XMILE, and I had no involvement (apart from some brief comments) on its development. The only reason for setting up the wiki was because I thought that might help to provide some momentum to the idea of having a community approach to developing an SD markup language (that turned out to be a mistaken optimism). The only reason why I invested time in making XMILE tools (Schema, converters, XSLT stylesheets) was because, again, I thought it would provide some momentum, and because I thought it was more important to have *a* SD markup language than spending time trying to make *the best* SD markup language - an exercise which would probably have again got bogged down and led nowhere.

I trust that no-one who is inte...

Statistics : Posted by Robert Muetzelfeldt • on Sun Jul 26, 2009 9:38 am • Replies 17 • Views 1274

Re: Very Basic Question

3351 — 2012-01-27T06:58:07-05:00

Dear Guido,

Your question on whether there is evidence 'out there that decisions and change has happened in a significantly better way using SD that it would have if SD had not been used' has been of interest to me for quite some time. I think there is some evidence. In 2002 Jac Vennix, Theo van Mullekom and I published a paper in System dynamics review that looked at 107 published cases on group model building. Group model building (GMB) is a generic term for building SD models with experts and/ or stakeholders. There were few studies comparing GMB to other interventions, and naturally those that do use a comparison group tend to build models with students. In those modeling projects there is no actual implementation and some authors (e.g. Colin Eden) argue that the decision making process in a student group is uncomparable to that of 'real' clients. So ideally you would like to have both a control group *as well* as real clients. The only examples that come to my mind are the studi...

Statistics : Posted by Etiënne Rouwette • on Thu Oct 20, 2011 6:25 am • Replies 13 • Views 290

Job Opening at IMA

3581 — 2012-01-26T12:20:24-05:00

There is a new job opportunity at Intelligent Modelling and Analysis Group (IMA). Link to the ad on the System Dynamics Society website(+).

Statistics : Posted by Roberta Spencer • on Sat Jan 10, 2009 1:01 pm • Replies 56 • Views 185955

Online Course in Model Thinking - Prof Scott E. Page

5454 — 2012-01-25T02:54:20-05:00

Dear all,

An online course in Model Thinking is due to start next month - see "http://www.modelthinker-class.org/"

The overview describes the context as:

"We live in a complex world with diverse people, firms, and governments whose behaviors aggregate to produce novel, unexpected phenomena. We see political uprisings, market crashes, and a never ending array of social trends. How do we make sense of it?

Models. Evidence shows that people who think with models consistently outperform those who don't. And, moreover people who think with lots of models outperform people who use only one"

If anyone is taking this online course, we can use this post to track progress and discuss any points of interest.

best regards,
Jim.

Statistics : Posted by Jim Duggan • on Wed Jan 25, 2012 2:54 am • Replies 0 • Views 40

Re: Is the forum moribund?

5454 — 2012-01-21T05:05:22-05:00

Hi all,

Tom - good and timely post, as it is a reminder of the challenge that our community faces in having a vibrant "go to place" for online collaborative discussions.

I don't think it's a technology issue at all, because the Forum provides most of the functions that are provided by linked in, and it does allow for more in-depth discussions in terms of longer and more reflective posts, and sharing images, files, etc.

Is the unique selling point of this forum that it is a place where all SD-related activity is highlighted. For example:

* for the upcoming conference, the programme committee and thread chairs could start discussion on the paper topics that they hope to receive.

* the Editorial Board of the SDR can give updates on the journal, average delay, backlog, special issues etc, and how to improve the impact factor

* the policy council could use the forum to communicate latest developments and get feedback from members

* senior thought leaders can encourage/pr...

Statistics : Posted by Jim Duggan • on Tue Jan 12, 2010 5:08 pm • Replies 23 • Views 1271

Re: Limits to Growth recent Boom and doom article

3272 — 2012-01-20T03:30:52-05:00

Sorry about that. Boo indeed. I should have checked the non-subscriber login more thoroughly. Waiting for activation now before correcting the original post.

Statistics : Posted by R. Joel Rahn • on Mon Jan 25, 2010 3:52 pm • Replies 22 • Views 4001

Change in online access for SDR

3581 — 2012-01-19T15:58:00-05:00

Announcing an important change to Society members' online access to the System Dynamics Review

Membership Services at our publisher, John Wiley & Sons, has implemented changes in online access to theSystem Dynamics Review. This year Wiley is migrating to a new access method, so there will be a fundamental change to access toSystem Dynamics Review works via the publishers’ website. New registration instructions will be sent directly by Wiley to all members. Please note that this applies to all System Dynamics Society members, even if those who have set up their access in the past under the old system. (The old access arrangement will be discontinued soon.)

The email message from Wiley will have the subject line: “Wiley Online Library Activation Instructions for Society Membership Online Access”). In order to continue online access to theSystem Dynamics Review,...

Statistics : Posted by Roberta Spencer • on Sat Jan 10, 2009 12:54 pm • Replies 24 • Views 20719

Limits to Growth 40th Anniversary Symposium in DC

3581 — 2012-01-19T15:53:30-05:00

Symposium: Perspectives on Limits to Growth: Challenges to Building a Sustainable Planet

To celebrate the 40th anniversary of the launching of Limits to Growth, the first report to the Club of Rome, a joint symposium entitled “Perspectives on Limits to Growth: Challenges to Building a Sustainable Planet” will be hosted in Washington, DC by the Club of Rome and the Smithsonian Institution’s Consortium for Understanding and Sustaining a Biodiverse Planet. Please see the program statement below.

The symposium will be held on Thursday March 1st, from 9:00 a.m. to 5:15 p.m. in the Rasmuson Theater of the National Museum of the American Indian at 4th Street and Independence Avenue, SW on the National Mall. A reception will follow. If you are interested in attending, please contact Consortia@si.edu for more information.

Program Statement: "Perspectives on Limits to Growth: Challenges to Building...

Statistics : Posted by Roberta Spencer • on Sat Jan 10, 2009 12:59 pm • Replies 27 • Views 21345

Limits to Growth 40 years later in New Scientist

3272 — 2012-01-19T02:01:42-05:00

There is an article in the Jan.7-13 2012 New Scientist: Boom and doom: Revisiting prophecies of collapse, an excellent brief survey and appreciation of The Limits to Growth 40 years after its first publication. The full article is only available to subscribers ($99CAD/yr) but should be available in a good science library.

The author is careful to note the most egregious mistaken interpretations encountered in the popular and academic press, particularly the false assertion that the World 3 model's results are predictions. Worth a read.

Statistics : Posted by R. Joel Rahn • on Sat Jan 10, 2009 1:03 pm • Replies 12 • Views 11407

Re: meaning of the next SDS conference topic

12716 — 2012-01-14T13:20:32-05:00

Upon reading what Sarah has written I felt a warm recognition of the lectures by Khalid Saeed that I had the chance to hear. I do well remember the stray dog example and the latent ressources nourishing something we do not want to have around. But it has been Khalid Saeed again that in his paper upon using PID-control made me conscious with regard to how and what to control(http://www.sciencedirect.com/science/article/pii/S0148296307003189 ). Here Khalid's message was not as far as I can remember that we should refrain from mechanistic, heartless control itself but to think about how to do it right, in order to reach stability in the system at hand.

The distaste regarding the (supposedly) mechanistic, heartless word "control" reminds me of Michael Pidd's intro in his bookTools for Thinking: Modelling in Management Science (the intro can be read here: http://www.amazon.de/Tools-Thinking-Modelling-Management-Science/dp/0470721421/ref=sr_1_cc_1?s=aps...

Statistics : Posted by Guido Reichert • on Wed Nov 30, 2011 4:19 am • Replies 7 • Views 343

Re: Conferences

3432 — 2012-01-14T05:36:25-05:00

EURO XXV Conference, 8-11 July 2012, Vilnius Lithuania

Dear Colleagues

This is an invitation for you to collaborate with the stream "System Dynamics Modelling and Simulation", at EURO XXV, to be held from 8 - 11 July 2012, in Vilnius, Lithuania. This is the 25th European Conference on Operational Research. The Conference theme - OR connecting sciences – emphasizes the inter- and even transdisciplinary nature of Operations Research.

The website can be found under "http://www.euro-2012.lt/". It offers a first demonstration of the scientific strength of this conference.

Being responsible for the stream "System Dynamics Modelling and Simulation", we would very much appreciate your contribution. The general purpose of this stream is to bring together works about the modelling and simulation of complex dynamic systems, based on the System Dynamics methodology. Contributions...

Statistics : Posted by Markus Schwaninger • on Sat Jan 10, 2009 12:51 pm • Replies 44 • Views 29878

Powersim Software: Studio 9 is now on sale

13908 — 2012-01-12T09:32:02-05:00

Powersim Studio has been transformed to support both 32-bit and 64-bit operating systems and increased its performance. It has also been given a user interfaceface-lift.

64-bit Platform Version:
-A new platform version of Powersim Studio targeting 64-bit Windows is now available, allowing for larger models and increased simulation performance.

Premium Edition:
-Powersim Studio 9 introduces the Premium edition targeted towards customers working with very large models.

Features:
-A presentation in Powersim Studio can now be augmented with up to four windows with HTML content, called Presentation Sidekicks. The sidekick windows allow you to add new visual elements and more dynamics to your presentations.
-You can now change the position of a legend for a Time Graph or Chart control.
-It is now possible to import values to start-up variables through datasets.
-In the Premium...

Statistics : Posted by Toralf Alsaker • on Sat Jan 10, 2009 1:02 pm • Replies 9 • Views 9051

Presentations on YouTube

2016 — 2011-12-22T05:32:14-05:00

Check out some recorded presentations from the UK Chapter's Feb 2011 annual meeting at youtube.com/uksystemdynamics. If you've not tried it before, it's pretty easy if you're not fussy about hi-fi audio - simply run a screen-capture program while the presentation is being given [we use Camtasia], then publish the resulting screen-cast. Will try to do this at all future Chapter events - just need to get formal permission from speakers to do it.

Statistics : Posted by Kim Warren • on Thu Dec 22, 2011 5:32 am • Replies 0 • Views 128

Prizes of the UK Chapter

2258 — 2011-12-12T15:07:27-05:00

This is a reminder of two prizes awarded by the UK Chapter of the International System Dynamics Society. Theclosing date for the next prize submissions is the13th of January 2012 . The winning submissions are chosen by the Policy Council of the UK Chapter of the System Dynamics Society and announced at the annual Gathering (9-10 February2012).

Steer Davies Gleave Prize
The Steer Davies Gleave Prize for System Dynamics is open to anyone living or working in the UK, and is offered for work carried out during the last two years. The aim of this prize is to promote the use of System Dynamics to address real-world problems, and to raise awareness of System Dynamics by publicising examples of such good work. Please see the Chapter website for moreinformation.

Student prize
We also wish to draw your attention to the Student Prize which is...

Statistics : Posted by Steffen Bayer • on Tue Jan 13, 2009 8:40 am • Replies 8 • Views 8565

Re: Feedback on new Obesity-related Stella (story-telling) M

5939 — 2011-12-05T10:58:44-05:00

Hi Tarek,

I applaud the effort and think obesity is timely and important topic. I also think the exploration of the energy balance equation is a great place to start. With that said, I hope my feedback is received as purely constructive.

There are number of issues with how things are laid out. The inconsistent navigation is quite confusing. I understand the desire to allow for non-linear navigation, but for a story like this I think you are best served by having forward and back navigation exclusively with a few possible side branches. Overall the presentation looks quite dated. I'm not sure if that is an artifact of Stella (perhaps an old version?), but in order to have broader appeal it really should look clean and modern. Along that line, why not online? Forio hosts small models of this size for free with more options for a fee. There are many good exampleshere ....

Statistics : Posted by Bruce Skarin • on Sat Dec 03, 2011 4:24 pm • Replies 1 • Views 108

New Obesity-related Stella (story-telling) Model Available

4422 — 2011-12-04T10:23:18-05:00

We are in the process of creating a series of obesity-related Stella/story-telling type models (referred to as Labs)… possibly 5 in all. The target is the general population as well as academics (both System Dynamics modelers as well as school-level educators on the frontlines of the childhood obesity fight).
Lab 1 is done… and is on The Energy Balance Equation—the staple energy calculus most dieters use (but shouldn’t) to manage weight-loss. It is posted for FREE download on:
"http://www.thinkingincirclesaboutobesity.com/Software.htm"

My goal/hope for Lab 1 is two-fold:

1. That it helps clarify some of the serious limitations/pitfalls of the Energy Balance Equation to a wide audience. And,

2. Garner feedback from System Dynamicists to help us fine-tune the interface/user experience for Labs 2 thru 5.

We put lots of bells and whistles in the interface (movies, sounds, e...

Statistics : Posted by Tarek Abdel-Hamid • on Sun Dec 04, 2011 10:23 am • Replies 0 • Views 130

Re: Modeling stakeholder's communication

5452 — 2011-11-22T12:11:17-05:00

I think some different search terms will get you on the right track.... I would suggest searching for "stakeholder analysis" with one, or two, additional search terms: "system dynamics" Vensim, stella, ... there is lots of literature on "stakeholder analysis", and this might lead to some useful information on stakeholder communication.

Statistics : Posted by Richard Dudley • on Sun Oct 09, 2011 9:55 am • Replies 4 • Views 243

Re: Software to identify feedback-loops

3032 — 2011-11-16T12:32:42-05:00

And an alternative approach to graph method is discussed in:

Consistency in explaining model behavior based on its feedback structure

which just appeared in early-view of system dynamics review
"http://onlinelibrary.wiley.com/journal/10.1002/(ISSN")1099-1727/earlyview

On the (feedback) structure of spreadsheet models, it seems to me that we are at the two extremes: One is having no visualization and explicit knowledge of the structure including feedback loops which is the case in spreadsheet models; and the other is having too much information on the details of the underlying structure. Until we find a proven way to get at the right amount of information about the structure, I will stick with the latter, and use intuition as filtering mechanism for the time being. "Let's not look because it is too much" doesn't seem like a strategy for learning and understanding.

Statistics : Posted by Mohammad Mojtahedzadeh • on Sun Nov 13, 2011 10:46 pm • Replies 8 • Views 435

Re: Modeling rational expectation

5515 — 2011-11-09T13:39:24-05:00

"Rational Expectations" is a rather broad concept. There are cases where the optimal forecast of a process is something simple like a SMOOTH, for example (seehttp://models.metasd.com/stochastic-processes/ ). In some cases you can model a forward-looking decision by analytically solving for the optimal decision given the current states in your model, and implement the result as a decision rule.

However, if you actually want to experiment with true forward-looking decisions, in which the agent actually uses information about the future, you need to use optimization (at least in SD tools that I'm aware of). Then the question is, how to formulate your decision rule? The obvious choices are (a) create some kind of feedback rule, like production = a*expected sales + b*(desired inventory-inventory) + ... and estimate the parameters, or (b) find an open loop decision as a function of time, either as a polynomial or a vector of points (using...

Statistics : Posted by Thomas Fiddaman • on Thu Oct 20, 2011 8:21 am • Replies 2 • Views 161

Anemia Management developed using System Dynamics

11233 — 2011-11-04T13:54:05-04:00

Mayo Clinic Doctors Team with System Dynamics Practitioners to Deliver Low Cost Personalized Care For the Management of Anemia Among Dialysis Patents

There are millions of patients worldwide who receive dialysis therapy for the treatment of End Stage Renal Disease. Because the kidneys of these patients cannot produce erythropoietin, the vast majority require the administration of synthetic form of the hormone. Erythropoietin, Iron, Folate, and Vitamin B12 interact dynamically with the process of red blood cell production. Imbalances among these “system variables” can lead to anemia as well as blood clotting and stroke. This two part video describes how a system dynamics model was used to create personalized dosing regimens for erythropoietin. Part 1 describes the model, part 2 describes the substantial improvements in patent quality of life and significantly reduced costs we have obtained. Mayo doctors are quoted as saying the novel approach used in this project “applies no...

Statistics : Posted by Gene Bellinger • on Fri Nov 04, 2011 12:54 pm • Replies 0 • Views 137

Re: controversy about a result in the wolrd3-03 model

5058 — 2011-10-31T12:41:31-04:00

Hi Bob.

Your reference to a differential approach, at least, brings light to the origin of the formulation as it politically justifies the approximation.

But I do not agree totally with your approach.

It is true, provided that the mortality is the same that the differential equation will be
(population / 15) * dt as the limit of the difference equation if the time step is decreasing to 0.
But the equation (population * (1 – (mortality * time step)) / 15) is right too even in the differential equation and has the advantage to be right too in the difference equation where the time step is larger.

But if you stick to the extreme hypothesis that all people die in a time step, you cannot erase the mortality * dt because the mortality is equal to 1/dt and the term with mortality is no more marginal compared with the other terms. In this case the error is increasing as the time step is decreasing.

I prefer a formulation that is always right, even if slightly more complex, wh...

Statistics : Posted by Jean-Jacques Lauble • on Sat Oct 29, 2011 10:01 am • Replies 5 • Views 171

Jorge Andrick Parra Valencia -- New PhD

3581 — 2011-10-26T21:52:16-04:00

Jorge Andrick Parra Valencia successfully defended his PhD dissertation, Construct for testing cooperation in large-scale social dilemmas, in October 2011. Professor Isaac Dyner was the Director-Advisor. Dr. Parra Valencia is a Faculty Professor, Systems Engineering Faculty, Systemic Thinking Research Group at the Universidad Autónoma de Bucaramanga, Colombia. Congratulations Jorge Andrick!

Statistics : Posted by Roberta Spencer • on Tue Jan 13, 2009 5:59 pm • Replies 2 • Views 6622

PhpBB Update

5463 — 2011-10-22T07:50:21-04:00

Hi Everyone,

I updated the forum to the current PhpBB version (3.0.9). It was not exactly a smooth update so if you run into trouble please let me know (bobeberlein at gmail if the inline mail option turns out to be one of the broken things).

Statistics : Posted by Robert Eberlein • on Sat Jan 10, 2009 1:36 pm • Replies 19 • Views 20026

Re: Parabola Shape

9797 — 2011-10-20T07:10:10-04:00

Thanks to everyone who responded. I have been playing with all these ideas and find the math all unsatisfactory. All the methods of lookups or equations seem to create a boundary or exogenous (subjective) input my model, whereas an explicit articulation of the structure of the system would be preferable.

As Tom wrote: "It seems that what must be going on in the real system must be somehow more complex than a first order outflow, and it would be good to explicitly capture the dynamics that yield the shape of the outflow."

Thus, I believe that the question to be explored further is - in project dynamics - am I correct in observing from some data that the work tends to be doled out in a up-side down parabolic shape (vs. s-shaped growth and decline)? If this observation is correct, is it significant? (I mean, the areas under the curves are pretty close in the two shapes). And, if it's a significant difference, what is the operational structure that causes this allocation of...

Statistics : Posted by Sarah Boyar • on Wed Sep 21, 2011 1:05 pm • Replies 4 • Views 175

Contact with SD academics / researchers in Sydney?

11333 — 2011-10-10T08:08:36-04:00

Good day

I wish to establish contact with academics / researchers who are active in system dynamics modelling based in Sydney, Australia. Can someone please provide me with leads?

Regards

Shamim Bodhanya
Leadership Centre
Durban, South Africa
bodhanyas1@ukzn.ac.za

Statistics : Posted by Shamim Bodhanya • on Mon Oct 10, 2011 7:08 am • Replies 0 • Views 113

Re: OR and project management

5515 — 2011-09-20T19:00:26-04:00

Are there online papers or abstracts? (The link above appears to be broken.)

Thanks,

Tom

Statistics : Posted by Thomas Fiddaman • on Mon Feb 21, 2011 9:55 am • Replies 3 • Views 473

People Express 2000 MFS

2116 — 2011-09-16T10:54:46-04:00

We are trying to set up a simulation exercise usingPeople Express 2000 Management Flight Simulator ("http://www.strategydynamics.com/microworlds/people-express/") at the Regional Conference in Brazil (November 16-18): "http://www.sdsbrazil.org/congreso.htm".If you are planning on attending this event , and you have experienced this simulation exercise, consider volunteering as a helper. We'll probably need 5-6 people in this role. If you consider yourself capable of conducting and debriefing the simulation exercise for a group of 50 people or more, please also let me know. (Although we invited an instructor, it is still pending confirmation.)

Unless you prefer to post here, please send your replies to me directly.

Thank you,

Aldo Zagonel