SD and other modelling approaches

fadl alakwa fadlmaster1 yahoo.co
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by fadl alakwa fadlmaster1 yahoo.co » Sat Dec 10, 2005 12:29 pm

Posted by fadl alakwa <fadlmaster1@yahoo.com>
Hello

System dynamics is the approach which was designed for study
complex system, to examine the structure of the system.
Is there any comparison between SD and others modeling approaches?
What are the important advantages of SD on other approaches?
What are the important drawbacks of SD?
REGARDS

Posted by fadl alakwa <fadlmaster1@yahoo.com>
posting date Fri, 9 Dec 2005 10:29:50 -0800 (PST)

Jay W. Forrester jforestr MIT.ED
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jay W. Forrester jforestr MIT.ED » Sun Dec 11, 2005 1:37 pm

Posted by ""Jay W. Forrester"" <jforestr@MIT.EDU>
Perhaps the following will be useful.

Information on System Dynamics
Jay W. Forrester
Information revised
February 4, 2005

System Dynamics Bibliography:

To order the system dynamics bibliography of over 4100 entries, specify IBM type PC, or Macintosh

System Dynamics Society
Roberta Spencer, Executive Director
Milne 300--Rockefeller College
State University at Albany
Albany, NY 12222 USA

tel: 1-518-442-3865Ý
fax: 518-442-3398
email: System.Dynamics@albany.edu

Three formats are available:

1. For Endnote, a very effective bibliography
software available for either Macintosh or PC
from:

ISI ResearchSoft
www.endnote.com
Tel: 760-438-5526

I use Endnote and recommend it and use it to search for the references.

2. An exported version with field delimiters that
presumably can be loaded into some other kind of
database.

3. A listing that one can look at in a word
processor and do some simple finding operations.

-----------------------------------------------

Membership in the System Dynamics Society and
subscription to the System Dynamics Review are
US$90 per year for regular members
and US$45 for students.
Send application to the System Dynamics Society (above)

To contact the office of the System Dynamics
Society and to order copies of the ""Beer Game""
group simulation exercise: tel: 1-518-442-3865
fax: 518-442-3398
email: System.Dynamics@albany.edu
----------------------------------------------

MIT history of system dynamics development:
>From the System Dynamics Society can be obtained
a DVD disk containing several thousand memos
written during the first several decades of
developing the field of system dynamics. The
disk also contains more than 200 theses that were
written in that same time period.


------------------------------------
The next annual international conference of the
System Dynamics Society will be in Boston,
Massachusetts, USA, July 17-21, 2005. Write to
the System Dynamics Society,

System Dynamics Society
Roberta Spencer, Executive Director
Milne 300--Rockefeller College
State University at Albany
Albany, NY 12222 USA
tel: 1-518-442-3865Ý
fax: 518-442-3398
email: System.Dynamics@albany.edu
----------------------------------------

The publisher for books in the following block
has changed from Productivity Press to Pegasus
Communications.

Pegasus Communications, Inc.
One Moody Street
Waltham, MA 02453-5339

Within the U.S
tel:1-800-272-0945
fax: 1-800-701-7083
Outside the U.S.
tel: 781-398-9700
fax: 781-894-7175
Web page: www.pegasuscom.com

Alfeld, Louis Edward, and Alan K. Graham. 1976.
Introduction to Urban Dynamics. Waltham, MA:
Pegasus Communications. 333 pp.

Forrester, Jay W. 1961. Industrial Dynamics.
Waltham, MA: Pegasus Communications. 464 pp.

Forrester, Jay W. 1968. Principles of Systems.
(2nd ed.). Waltham, MA: Pegasus Communications.
391 pp.

Forrester, Jay W. 1969. Urban Dynamics. Waltham,
MA: Pegasus Communications. 285 pp.

Forrester, Jay W. 1971. World Dynamics. (1973
second ed.). Waltham, MA: Pegasus Communications.
144 pp. Second edition has an added chapter on
physical vs. social limits.

Forrester, Jay W. 1975. Collected Papers of Jay
W. Forrester. Waltham, MA: Pegasus
Communications. 284 pp .

Forrester, Nathan B. 1973. The Life Cycle of
Economic Development. Waltham, MA: Pegasus
Communications. 194 pp.

Goodman, Michael R. 1974. Study Notes in System
Dynamics. Waltham, MA: Pegasus Communications.
388 pp.

Lyneis, James M. 1980. Corporate Planning and
Policy Design: A System Dynamics Approach.
Waltham, MA: Pegasus Communications. 520 pp.

Mass, Nathaniel J., ed., 1974. Readings in Urban
Dynamics: Volume I, Waltham, MA: Pegasus
Communications, 303 pp.

Mass, Nathaniel J. 1975. Economic Cycles: An
Analysis of Underlying Causes. Waltham, MA:
Pegasus Communications. 185 pp.

Meadows, Dennis L. 1970. Dynamics of Commodity
Production Cycles. Waltham, MA: Pegasus
Communications. 104 pp.

Meadows, Dennis L., et al. 1974. Dynamics of
Growth in a Finite World. Waltham, MA: Pegasus
Communications. 637 pp.

Meadows, Dennis L., and Donella H. Meadows, ed.,
1973. Toward Global Equilibrium: Collected
Papers, Waltham, MA: Pegasus Communications, 358
pp.

Morecroft, John D. W., and John D. Sterman, ed.,
(1994). Modeling for Learning Organizations,
Waltham, MA: Pegasus Communications, 400 pp.

Randers, Jorgen, ed., 1980. Elements of the
System Dynamics Method, Waltham, MA: Pegasus
Communications, 488 pp.

Richardson, George P., and Alexander L. Pugh III.
1981. Introduction to System Dynamics Modeling
with DYNAMO. Waltham, MA: Pegasus Communications.
413 pp.

Roberts, Edward B. 1978. Managerial Applications
of System Dynamics. Waltham, MA: Pegasus
Communications. 562 pp.

Roberts, Nancy, David Andersen, Ralph Deal,
Michael Garet, William Shaffer. 1983.
Introduction to Computer Simulation: A System
Dynamics Modeling Approach. Waltham, MA: Pegasus Communications, 562 pages .

Schroeder, Walter W., III, Robert E. Sweeney, and
Louis Edward Alfeld, ed., 1975. Readings in Urban
Dynamics: Volume 2, Waltham, MA: Pegasus
Communications, 305 pp.

---------------------------------------------------
Books from other publishers include:

Coyle, R. G., 1996. System Dynamics Modelling--A
Practical Approach, London: Chapman & Hall. 413
pp.

Fisher, Diana M. (2001). Lessons in High School
Mathematics: A Dynamic Approach. Hanover, NH,
isee Systems, Inc.

Fisher, Diana M. (2005). Modeling Dynamics
Systems: Lessons for a First Course. Hanover, NH,
isee Systems, Inc.

Ford, Andrew, 1999. Modeling the Environment: An
Introduction to System Dynamics Modeling of
Environmental Systems, Washington, D.C.: Island
Press. 415 pp.

Mandinach, Ellen B., and Hugh F. Cline, 1994.
Classroom Dynamics: Implementing a
Technology-Based Learning Environment, Hillsdale,
NJ: Lawrence Erlbaum Associates. 211 pp.

Richardson, George P., 1991. Feedback Thought in
Social Science and Systems Theory, Waltham, MA,
Pegasus Communications. 374 pp.

Richardson, George P., 1996. Modelling for
Management: Simulation in Support of Systems
Thinking, Brookfield, Vt.: Dartmouth Publishing.
493 & 447 pp.

Sterman, John D. (2000). Business Dynamics:
Systems Thinking and Modeling for a Complex
World. New York: Irwin: McGraw-Hill. 982 pp.

----------------------------------
A self-study guide to system dynamics, called
""Road Maps,"" is available for downloading from:

http://sysdyn.clexchange.org

or in paper copy from:

Creative Learning Exchange
Ms. Lees Stuntz, Director
1 Keefe Road
Acton, MA 01720, USA
tel: 1-508-287-0070
fax: 1-508-287-0080
email: stuntzln@tiac.net
------------------------------------------------

For those wanting information on introducing
system dynamics in kindergarten through 12th
grade education:

1. The Creative Learning Exchange is a nonprofit
foundation that acts as a clearinghouse to
provide information on system dynamics in
precollege education and to help teachers share
their experiences. They can be reached at:

Creative Learning Exchange
Ms. Lees Stuntz, Director
1 Keefe Road
Acton, MA 01720, USA
tel: 1-978-287-0070
fax: 1-978-287-0080
email: stuntzln@tiac.net
web: http://www.clexchange.org

2. The System Dynamics in Education Project at
MIT has transferred its web page to the Creative
Learning Exchange at http://sysdyn.clexchange.org

3. An Internet discussion group on K-12 issues
related to system dynamics can be joined:
Contact: StuntzLN@CLEXCHANGE.ORG
To subscribe,
Please provide the following information:
First Name:
Last Name:
E-mail:
Title:
Address:
City:
State or Province:
ZIP or Postal Code:
Country:
Day Phone Number:
Evening Phone Number:
Fax Number:

5. The summer 93 issue of the System Dynamics
Review, vol 9 no. 2, was a special issue on
""Systems thinking in education"" It contains many
interesting pieces including reports from the
field by teachers.

----------------------------------------------

There are now three good software packages for
system dynamics. You can request information:
--------------------------------------------
STELLA for Macintosh or PC:

High Performance Systems
45 Lyme Road, Suite #300
Hanover, NH 03755, USA

Phone: 1-603-643-9636 customer support
tel: 1-800-332-1202 product inquiries
fax: 1-603-643-9502
email: support@hps-inc.com
http://www.hps-inc.com/

--------------------------------------
Powersim for PC:

Powersim Corporation
1175 Herndon Parkway Suite 600
Herndon, VA 20170
Phone: (703) 481-1270
Fax: (703) 481-1271
Email: powersim@powersim.com
http://www.powersim.com

Norway Address:
Powersim AS
PO Box 206
N-5100 Isdalstø
Phone: +47 56 34 24 00
Fax: +47 56 34 24 01
Email: powersim@powersim.no
http://www.powersim.no
-------------------------------------------

Vensim for PC or Macintosh:

Ventana Systems, Inc.
149 Waverley Street
Belmont, MA 02178, USA

tel: 1-617-489-5249
fax: 1-617-489-53316
email: vensim@world.std.com
http://www.vensim.com/

A ""Personal Learning Edition"" of Vensim and its
manual can be downloaded free from:
http://www.vensim.com/ This downloadable Vensim
PLE is the one used for teaching system dynamics
at MIT.
-- ---------------------------------------------------------
Jay W. Forrester Professor of Management Sloan School Massachusetts Institute of Technology Room E60-156 Cambridge, MA 02139 Posted by ""Jay W. Forrester"" <jforestr@MIT.EDU> posting date Sat, 10 Dec 2005 14:48:15 -0500

Jim Duggan jim.duggan nuigalway.
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jim Duggan jim.duggan nuigalway. » Mon Dec 12, 2005 12:14 pm

Posted by Jim Duggan <jim.duggan@nuigalway.ie>
Hi,

A couple of books that describe system dynamics within the context of systems thinking approaches are:

Robert Flood and Michael Jackson. ""Creative Problem Solving: Total Systems Intervention."" Wiley 1991.

Jonathan Rosenhead, John Mingers. ""Rational Analysis for a Problematic World Revisited."" Wiley 2001. 2nd Edition.

regards,
Jim.
Posted by Jim Duggan <jim.duggan@nuigalway.ie>
posting date Mon, 12 Dec 2005 09:08:41 +0000

Magne Myrtveit magne myrtveit.co
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Magne Myrtveit magne myrtveit.co » Mon Dec 12, 2005 12:19 pm

Posted by ""Magne Myrtveit"" <magne@myrtveit.com>
Hello,

The following is really worth reading in connection with all three question that you pose:

Meadows, Donella H. 1980. The Unavoidable A Priori. In Elements of the System Dynamics Method, edited by J. Randers. Cambridge MA: Productivity Press.Bergen.

If you are interested in controversy between diciplines, maybe you'll find the following worth reading:

Myrtveit, M. 2005 The World Model Controversy. ISSN 1503-4860. WORKING PAPERS IN SYSTEM DYNAMICS. University of Bergen. http://www.ifi.uib.no/sd/wp.html

Regards,
Magne Myrtveit
Posted by ""Magne Myrtveit"" <magne@myrtveit.com>
posting date Mon, 12 Dec 2005 08:45:43 +0100

Justin Lyon justin1028 yahoo.com
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Justin Lyon justin1028 yahoo.com » Tue Dec 13, 2005 12:01 pm

Posted by Justin Lyon <justin1028@yahoo.com>
>> http://www.ifi.uib.no/sd/wp.html

I've read Magne's _The World Model Controversy_ It's
excellent. I strongly recommend reading it!

-Justin
Posted by Justin Lyon <justin1028@yahoo.com>
posting date Mon, 12 Dec 2005 05:09:32 -0800 (PST)

geoff coyle geoff.coyle btintern
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by geoff coyle geoff.coyle btintern » Wed Dec 14, 2005 11:03 am

Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
This is an interesting correspondence though it does not seem to have answered the original question, which was about SD and other modelling approaches. In that context I have always felt that one cannot do good SD without at least a nodding acquaintance with the wide variety of modelling approaches that are available. In particular, one needs to understand the important difference between SD and discrete event simulation (DES).

Some good references are:

Professor Mike Pidd's excellent text on DES and SD. I think the title is 'Simulation Modelling', but it is published by Wiley.

Another excellent source is Professor Pat Rivett's outstanding 'The Craft of Decision Modelling', also Wiley. Its great strengths are the author's vast experience and the fact that just about the only numbers in it are those on the pages!

Finally, there are any number of texts on operational research/management science. One, for instance, is H Taha's 'Operations Research'. It's not for the mathematically daunted, but it will tell you at least as much as you want to know about mathematical programming, queuing theory, and much else, including simulation. There are many similar texts, though I have yet to find one that even mentions SD. I wonder why that is.

Regards,

Geoff

Visiting Professor of Strategic Analysis,
University of Bath
Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
posting date Tue, 13 Dec 2005 12:20:55 -0000

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Thu Dec 15, 2005 12:02 pm

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi everybody.

Fadl asked a difficult question.
Instead of listing many advantages or drawbacks that will automatically bring contestations and complexity, I tried to figure out the main advantage and the main drawback, that seem to me evident. Both are big, being the bigger in its category. The advantage: it looks like the more powerful mathematical tool I know of that can 'in theory' resolve about any kind of problem, as the world is made of multitudes of stocks, rates and has the 'theoretical possibility' to simulate the world exactly as it works. The drawback: it comes from the advantage: the tool needs a lot of previous knowledge and experience to be used, and every problem a little complex needs time too to be resolved.

The advantage is quite evident at the first look. The drawback not. That should in theory attract many newcomers that are not aware of the drawback and should cause many of them to leave later on once the drawback begins to act on the results of their work.

I have no idea if this happens in reality, so I can be completely wrong. But not knowing the facts I can only speculate.

There is in the Vensim modelling guide a very interesting model relative to the growth of the SD field and to my opinion it lacks something that makes it highly biased to my opinion. Some people meet SD practitioners and a percentage is interested for further instruction. They become then training practitioners, then depending on some factors and after a while new practitioners and then again after a while experienced practitioners. But once somebody has become a training practitioner becoming an experience practitioner is only a question of time, and nobody is supposed to leave the aging chain. I do not know any field that has this particularity and from what I wrote previously, this percentage of leaving individuals can be high. Regards. J.J. Laublé Allocar Strasbourg France Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Thu, 15 Dec 2005 11:27:29 +0100

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Thu Dec 15, 2005 12:04 pm

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi everybody

Geoff writes
<This is an interesting correspondence though it does not seem to have <answered the original question, which was about SD and other modelling <approaches. In that context I have always felt that one cannot do good SD <without at least a nodding acquaintance with the wide variety of modelling <approaches that are available.

I agree completely. The original question was not answered.
I would add that before using SD with a problem, a potential good idea would be to have already experienced other techniques with it, so as to have a good understanding of it prior to any use of SD. I feel that SD is an expensive technique that should be used with care.

<Another excellent source is Professor Pat Rivett's outstanding 'The Craft of <Decision Modelling', also Wiley. Its great strengths are the author's vast <experience and the fact that just about the only numbers in it are those on <the pages!

I have bought the book and read it slowly when I have the time. It is the only book I have read so far that addresses down to earth cases with very simple tools: no linear programming, no optimization, no sophisticated tools, and it works. For an academic bravo!

It imples the following question: what is modelling?
I feel that when one thinks about any problem one makes some kind of modelling. So the question about SD modelling and other approaches could be extended and be: To what level of complexity is it necessary to model a problem?

<There are many similar texts, though I have yet to
<find one that even mentions SD. I wonder why that is.
I wonder too but could not find either the answer.
Regards.
J.J. Laublé Allocar
Strasbourg France
Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Wed, 14 Dec 2005 14:03:57 +0100

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Fri Dec 16, 2005 12:29 pm

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi everybody

The drawback I described in my last post, is not depending only on the experience of modellers but is too very depending on the kind of subject. It seems evident but it is better to mention it. The fact that it depends highly on the quality of the modellers and the type of problem, makes any other drawback very subjective.

The advantage and the drawback are good candidates for the explanation of two characteristics of SD. 1. The subject is subject to high controversy. (See the paper of Magnus
Myrtveit)
The experiences made will be very diverse depending on the problem and the modellers especially because the advantage (its universal possibility) will tend people to use it whatever their experience and the kind of problem.

2. Both advantage and drawback may be too an important reason of the too small growth of the field. The advantage pushes people to use the tool and the drawback may discourage them later on, loading a stock of people that have tried the tool but were not satisfied. How is this stock now? Is it growing or decreasing, what was its history in the past? What is its influence on the growth of the field? Regards. J.J. Laublé Allocar Strasbourg France Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Thu, 15 Dec 2005 16:11:40 +0100

geoff coyle geoff.coyle btintern
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by geoff coyle geoff.coyle btintern » Sat Dec 17, 2005 1:27 pm

Posted by ""geoff coyle"" <geoff.coyle@btinternet.com> Jean-Jacques also questions why the great majority of operations research/management science texts do not mention SD. Those that do often lump it with simulation in general. In other words, SD has been in existence now for practically 50 YEARS, but is seemingly ignored by those whom we would see as our peers in the analytical community. That is, perhaps, something that the SD community ought to take very seriously.

I do not know the reason for this. Indeed, it unlikely that there is a single cause, though it may be that our world view has something to do with it. Some correspondents have used phrases such as 'the world is made up of stocks and flows'. To be sure, a stock/flow viewpoint, that emphasises continuity is a powerful viewpoint for some classes of problem but to imply, as 'made up' does, that it is the only viewpoint is damaging to SD, because it is patently untrue. Another viewpoint is that the world also contains random and discrete events, which is why people as clever as us have invented Discrete Event Simulation, DES, for that class of problem.

Of course, one can see the queue in a supermarket as a stock that is fed and depleted by flows but, for issues such as the probability that customers will have to wait more than a certain time, or that the queue will exceed a given length, which are extremely important for that type of business, we have queuing theory. In fact, queuing theory offers important insights, but practical queuing problems, such as the 28 checkouts at my local supermarket, are usually addressed by DES.

It is also useful to see the world as a set of constraints, which is why we have linear programming for production planning in oil refineries, and similarly rather vital problems.

In a similar vein, I have four leading corporate strategy texts on my bookshelf, none of which mentions SD.

We cannot wish these phenomena away, neither can we avoid them by huddling together in what other people see as a closed and exclusive 'SD community'.

Regards,

Geoff

Visiting Professor of Strategic Analysis,
University of Bath
Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
posting date Fri, 16 Dec 2005 10:32:53 -0000

fadl alakwa fadlmaster1 yahoo.co
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by fadl alakwa fadlmaster1 yahoo.co » Sat Dec 17, 2005 1:27 pm

Posted by fadl alakwa <fadlmaster1@yahoo.com>
Hello

After I read the controversy paper I have knowledge that the SD was
not designed for predication purpose. Because it used an average
parameters from the literature, which sometimes difficulte to get it.

I do not know why SD is not considering with curve fitting technique.
I believe SD is strong in testing theories.

Regards
Posted by fadl alakwa <fadlmaster1@yahoo.com>
posting date Fri, 16 Dec 2005 04:47:12 -0800 (PST)

Jay Forrest systems jayforrest.c
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jay Forrest systems jayforrest.c » Sun Dec 18, 2005 1:47 pm

Posted by ""Jay Forrest"" <systems@jayforrest.com>
Hi Geoff!

What a great post! Lots of good things to think about!

My work has led me to view part of the ""SD problem"" to over a hundred years of reductionist focus by education - and in particular as a barrier to profitable consulting, in business schools.

The reductionist focus is immediately at odds with the holistic, spartan perspective of SD (minimal model to explain the question at hand). And the agglomeration/minimalization denies the lower level details reductionists want to ""see"". As we all know on this listserve, more detailed (with more model elements) invites its own set of problems, but I believe the bulk of our potential clients see SD as too spartan and thus discount it.

I think other simulation approaches also tend to view SD as ""spartan"". While we all know of models with a thousand or more elements, the stylized modeling of SD (which is somewhat less ""literal/realistic"" than say a typical refinery simulation and far less so than an agent model of a grocery
store) tends to diminish the regard the broader simulation community may hold for SD. Like all/most of us I find that troublesome for I firmly believe the SD approach has many advantages.

To date, growing computer power has generally enabled more and more detailed modeling, but the time requirement to develop and understand LARGE models is probably exponential with model size. While I think both DES and agent modeling will continue to gain use, I tend to believe that the boundary and assumption limitations of detailed models are beginning to show - particularly in business use. I think chinks in the values of both reductionist thinking and LARGE modeling are quite visible. They simply are not meeting the business demands of turbulence associated with globalization. I firmly believe the days of reductionist thinking are ending and that the successful will have to be holistic - or at least a combination of holistic/reductionistic.

A challenge for SD, I think, is to define the boundaries and assumptions in a way that truly captures the key elements of the future and not just the past/present so as to maximize the FUTURE value of the model.

Thank!
Jay Forrest
Posted by ""Jay Forrest"" <systems@jayforrest.com>
posting date Sat, 17 Dec 2005 09:31:25 -0600

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Sun Dec 18, 2005 1:52 pm

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi everybody

Geoff writes
<Some correspondents have used phrases such as 'the world is made up of <stocks and flows'. To be sure, a stock/flow viewpoint, that emphasises <continuity is a powerful viewpoint for some classes of problem but to imply, <as 'made up' does, that it is the only viewpoint is damaging to SD, because <it is patently untrue.

I do believe that as long as it is considered as strictly causal the world is made of a myriad of stocks (its state) and whose variations (the rates) are explained by the past level of stocks plus the rules that govern our world.

I do not understand why this view point should necessarily imply that it is absolutely necessary when thinking about something one should refer to the way it actually intimately works. If it was the case any mathematical problem would need differential equations to be resolved. I have to make decision in my business every days and Thanks God I never refer to any stock and flow considerations.

I do not see either why the stock and flow view point should necessarily be only continuous. I do not know very well DES but it is true that it does not consider feed back loops that are mainly based on the existence of stocks. Some software consider stocks and still have no feed back loops (Extend). I have never really understood why DES does not consider feed backs and how it can even produce relevant results when eluding this question.

What Geoff maybe thinks is that the stock and flow view point implies for many people the strict observance of this paradigm whatever the way you model a problem. If the people outside of the SD community think this way it may be too that the SD community is too strict about the use of its paradigm. One prove of this excessive rigor can be seen in the software used by the SDer. All the software and in particular Vensim with which I work, do not consider the possibility to work with one period of time and subsequently with no stocks. One can do it but with two periods and no stock.

Of course there is no more dynamic. And then? As long as you can solve some problems, why does it matter? This way of thinking would help build a bridge between the dynamic way to see things and the static way. To my point of view there is as much difference between a zero stock model (no dynamic) and one stock model and one stock model and a two stock model. Adding a stock adds a new dimension to the dynamic whether you start with a zero stock or a 10 stocks. The important thing to consider is the effect of the add-in stock on the previous model.

I remember to have exposed that problem to Bob Eberlein when I studied a distance course at Mit, three years ago. I pointed out that some people are more clever and have reversed the problem. They have constructed a software that is roughly an influence diagram that is static and added the possibility to work on periods. When you study their tutorial, all the chapters are on the static part and only the last is on the dynamic side. I bet that the 95 % of the users only deal with the static part which can already do a lot of nice job. I prefer not too give the reference of the software here as it is not the place for this. I agree fully with Geoff when he says that the SD community should try to understand why SD is ignored by a lot of books that deal with management sciences, decision sciences etc... It is particularly surprising as SD is an extremely rigorous scientific method. Regards. J.J. Laublé Allocar Strasbourg France. Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Sat, 17 Dec 2005 15:45:18 +0100

Richard Turnock richardturnock c
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Richard Turnock richardturnock c » Mon Dec 19, 2005 11:49 am

Posted by ""Richard Turnock"" <richardturnock@comcast.net>
>If you are interested in controversy between diciplines, maybe you'll
>find the following worth reading:
>
>Myrtveit, M. 2005 The World Model Controversy. ISSN 1503-4860. WORKING


I began learning SD in the summer of 1997 and I immediately began teaching high school teachers about SD that fall. Of course as I taught, I really started to learn SD. This past winter and summer I had the opportunity to work with graduate students taking Wayne Wakeland's System Dynamics class at Portland State University.

I learned more about modeling techniques over the years in workshops and conferences with the world leaders in the SD field. I continue to learn about how systems work. But one thing always confused me. Why was there this constant undercurrent and vague references to ""critics of SD"" or ""the controversy"" about SD?

Then Saturday morning, I read the paper by Magne Myrtveit. I think this paper should be required reading for every SD student and practitioner. ""Ah-ha"" moment for me like learning how a system works using an SD model.

Richard Turnock
Posted by ""Richard Turnock"" <richardturnock@comcast.net> posting date Sun, 18 Dec 2005 11:06:00 -0800

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Mon Dec 19, 2005 11:50 am

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi everybody


Jay writes in his last post


<but I believe the bulk of
<our potential clients see SD as too spartan and thus discount it.


This is certainly the heart of the SD problem, but do the potential clients dislike the Spartan characteristic because they think it is not reliable or because it is difficult to achieve?



We all know that it is very difficult to achieve and is particularly necessary as the

boundaries of the model is expanding and the number of loops with it.



The ability to spot the main influences and think with Pareto laws in the back of the mind is a rare quality that to my opinion can only be developed with experience and not in books.

This is why before trying to implement optimization schemes in the software, developers should have privileged the faculty to spot dominant loops, right at the level of the conceptual diagrams. That should be a critical tool to help staying Spartan!


Of course people used to discreet simulation and its consideration with details, will always have a tendency to discredit SD, but easing to stay Spartan may help considerably to build useful models and show that even such a model can give reliable results.

Regards.

J.J. Laublé Allocar
Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Sun, 18 Dec 2005 16:06:14 +0100

Kim Warren Kim strategydynamics.
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Kim Warren Kim strategydynamics. » Mon Dec 19, 2005 11:56 am

Posted by ""Kim Warren"" <Kim@strategydynamics.com>
Jean-Jacques asks ""why it is absolutely necessary when thinking about something one should refer to the way it actually intimately works."" Whilst not wishing to be dogmatic about it being 'absolutely necessary', there do seem to be a couple of advantages to favouring such a choice.

Firstly, it should help our models - as Geoff Coyle has said - 'do what the real world does, and for the same reasons'. This has two advantages [a] if something changes about the real-world situation we are studying, then our model does not become immediately irrelevant, but can be adapted quickly to follow the evolving situation and we can not only show that our 'answer' matches reality, but also that all the pieces that lead to the answer do too. Someone once pointed out to me, for example, that a big advantage of the Bass diffusion model of new-product introductions over other forecasting methods is its ability to anticipate turning points, as the reinforcing growth of product uptake runs out of potential customers for the product.

Secondly, using models that mimic reality should ease the learning path. I think you would have to be super-smart to look at a problem and develop a model of its solution by using an approach that does not match its inherent 'physics'. Not only would you have to be expert in the method itself, but also in translating the situation into terms that your method can handle, and then translating the solution back again into terms that the problem owner can recognise. And the chances that the problem owner themselves could ever replicate your work would be minimal.

Though I recognise the assertion that the world is made up of stocks and flows that accumulate, I have not seen anyone in this discussion add the further condition that these must accumulate *in a continuous manner* - or have I missed it?. As I understand it, SD itself is approximating if it treats all flows as continuous, which gets increasingly inaccurate, the more lumpy the flows are.

And does an SD model *have to* treat all flows as continuous in any case? The SD software tools do make it possible to represent discrete phenomena. Could we, for example, build a perfectly reasonable, simple queuing model in SD software - or is that entirely frowned upon? Just how unacceptable is it to include discrete events in SD models, and does anyone have examples of good work they have done or seen that uses SD this way?

[None of the above, by the way, is meant to imply that SD is 'superior' to DES, or to any other modeling approach that is well-suited to a particular problem situation.]

Kim Warren
Posted by ""Kim Warren"" <Kim@strategydynamics.com>
posting date Mon, 19 Dec 2005 09:15:01 -0000

Jean-Jacques Laublé jean-jacques
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Jean-Jacques Laublé jean-jacques » Tue Dec 20, 2005 12:09 pm

Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> Hi Kim

I agree with 'nearly' everything you wrote.
I never said that modelling the problem as it is really is not a good solution. I said it is as long as it is possible to do it, and as long as you do it correctly, meaning that you have the capacity to do it and that the problem suits this approach.

If something changes in the real world situation why should other methods not be able to take this change into account?

The diffusion model is one of the best demonstration of the power of SD, may be with aging chains. But not all problems can be translated in these well known applications unfortunately.

And suppose you are right. How does it come that this is not widely recognized?

The problem of continuity was exposed by Geoff I think.

You write
<[None of the above, by the way, is meant to imply that SD is 'superior' <to DES, or to any other modeling approach that is well-suited to a <particular problem situation.]

By writing this you seem to be in contradiction will all what was written before! This is what I was wanted to say. SD has competitors, and it seems that most people seem to believe that SD is so badly suited to any kind of problems that it is not necessary to mention it. I do not know if it is the same in England, but in France you can go to a bookstore and look at many books dealing with strategy for instance, and find no books that use the stock and flow representation, although it is often implicit and formulated in a literary form.

<secondly, using models that mimic reality should ease the learning path. < think you would have to be super-smart to look at a problem and develop a <model of its solution by using an approach that does not match its inherent <physics'.

When Kepler described the 'Kepler laws' he did not know anything about gravity. And when Newton described gravity he did not know anything about relativity that explains gravity by space curvature. And probably there is something behind relativity too.

Regards.
J.J. Laublé Allocar
Strasbourg France.
Posted by =?iso-8859-1?Q?Jean-Jacques_Laubl=E9?= <jean-jacques.lauble@wanadoo.fr> posting date Mon, 19 Dec 2005 14:12:21 +0100

Tobias Lorenz space56 freenet.de
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Tobias Lorenz space56 freenet.de » Wed Dec 21, 2005 11:49 am

Posted by ""Tobias Lorenz"" <space56@freenet.de>
Hey Everybody,

I am fairly new to the list (two days to be exact), but unfortunately well acquainted with the problem (as far as i see it at least) ;) One main task in eyes would or should be to collect the opposing simulation methodologies in a first step in order to identify the key difference. Is it SD opposing discrete simulation techniques (DES or even ABM) or is SD opposing econometrics? Or are DES and ABM too different again to be clustered together? The next task (in my eyes at least) would then be to identify the criteria for the usage of a specific methodologies. I disagree with the position that the choice of methods is a purely subjective preference of the modeller. Also in this discussion it has been mentioned that ""[...] you would have to be super-smart to look at a problem and develop a model of its solution by using an approach that does not match its inherent 'physics'."" So a handy thing to have would be an idea of how to fit certain physics with a specific methodology. Those criteria have not been developed up to now are does anyone have an idea of where to look for that? This would make my current work a lot easier...

Tobias Lorenz
DaimlerChrysler Research and Technology
Posted by ""Tobias Lorenz"" <space56@freenet.de>
posting date Tue, 20 Dec 2005 16:13:21 +0100

Bill Harris bill_harris facilita
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Bill Harris bill_harris facilita » Wed Dec 21, 2005 11:59 am

Posted by Bill Harris <bill_harris@facilitatedsystems.com>
""geoff coyle geoff.coyle btinternet.com"" <system-dynamics@VENSIM.COM> writes:
>> We cannot wish these phenomena away, neither can we avoid them by
>> huddling together in what other people see as a closed and exclusive
>> 'SD community'.


Geoff,

I've a theory, although I have no way of proving it at this time. I think many of us may aspire to becoming recognized experts in the field, teaching or consulting using SD.

I wonder if we'd have more luck if we decided SD was a useful tool for many a problem we face in business, in organizations, and in society, and we applied it in the places we find ourselves.

For example, say we work in a company. I suspect (but don't know) that we might try to sell management on the utility of SD as a tool for strategy development. We might try to get an internal position as the SD consultant for the company, or we might even quit and set up our own company.

What if instead we reached for SD for specific problems we faced and then provided the answer to the company? Certainly we might have to persuade our small group (task force, committee) to go down the path of trying SD as one of the approaches we'd use, but we'd be trying it on specific issues and seeing what results we get, not asking for a commitment in advance of producing anything.

By analogy, I used to work at a company that taught many people the Kepner-Tregoe approach to decision making and problem solving. We didn't bring in an expert to make decisions for us; we simply applied it ourselves, when we thought it was appropriate. (Okay, someone sold the company it was worth investing in the training, and I didn't see that
part.)

It may not be as exciting or glamorous to be a contributor to strategy or process design or operations or product development as it would be to be a known expert in the field, but it might get the field accepted more rapidly.

Some of us are on the outside already, obviously, but I still think the principle may hold. Instead of selling SD simulation to (most) prospects, what if we listened and sold excellence in problem solving or strategy development or ...? When enough people begin to notice better results than they might have expected and discover there's something called SD behind it, that might have more impact. (Of course, if they discover worse results, then we have some work to do on our side.)

And, as you said, Geoff, horses for courses.

Thoughts?

Bill
- --
Bill Harris http://facilitatedsystems.com/weblog/
Facilitated Systems Everett, WA 98208 USA
http://facilitatedsystems.com/
Posted by Bill Harris <bill_harris@facilitatedsystems.com>
posting date Tue, 20 Dec 2005 22:06:01 -0800

geoff coyle geoff.coyle btintern
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by geoff coyle geoff.coyle btintern » Thu Dec 22, 2005 12:03 pm

Posted by ""geoff coyle"" <geoff.coyle@btinternet.com> Jean-Jacques Lauble wrote:

"" I do not know if it is the same in England, but in France you can go to a bookstore and look at many books dealing with strategy for instance, and find no books that use the stock and flow representation, although it is often implicit and formulated in a literary form.""

It IS the same here.

Browsing the management science and strategic management sections of Blackwells in Oxford and London Business School bookshop produced NOTHING that even mentioned SD in the index. Of course, I didn't look at every single book, so there may be some exceptions, but they must be few and far between.

This should be deeply worrying for the SD community.

Firstly, we must ask why the much larger OR/management science community (some tens of thousands of people worldwide) does not see SD as a useful methodology on a professional par with mathematical programming, queuing theory etc? The annual conference of the UK-based Operational Research Society attracts hundreds of people and scores of papers, but only a handful of either will be SD. Why? Is it the same for other OR/MS conferences?

Secondly, strategic management is a core subject for every MBA student in the world, and I would hate even to guess how many that is every year, though a quarter of a million must be the lower limit (5000 business schools each with an intake of 50 gives that number, and many are very much larger). I know that there are some exceptions but, in practical terms, effectively none of these encounters SD from teachers or texts. Why?

Could it be that, despite what is claimed, SD does not do strategy? John Powell and I argued at Palermo that SD can be good at evaluating and exploring a pre-chosen strategic concept but it does not, indeed, cannot, evolve such concepts as that happens in a socio/political world that is external to SD's frame of reference. I daresay that that comment will create a storm, but storms don't address fundamental, and deeply worrying, concerns.

The hard fact is that SD is now virtually 50 years old. Many people use it, or have used it, but it is not in the mainstream of OR/MS or strategic management, both of which seem to be natural homes for SD. Can we, or you, since I am now 'retired', face up to that without controversy among ourselves?

Regards,

Geoff

Visiting Professor of Strategic Analysis,
University of Bath
Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
posting date Wed, 21 Dec 2005 10:46:43 -0000

Swanson John John.Swanson sdgwor
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Swanson John John.Swanson sdgwor » Thu Dec 22, 2005 12:03 pm

Posted by ""Swanson, John"" <John.Swanson@sdgworld.net>
Bill Harris wrote:
""I wonder if we'd have more luck if we decided SD was a useful tool for many a problem we face in business, in organizations, and in society, and we applied it in the places we find ourselves.""

I have to agree. I've long thought that trying to sell a technique like SD without focusing on an area of application can look quite weak to potential clients. You risk looking naive, or that you are offering a general solve-it-all technique that they can't quite credit. I think a better approach is to develop expertise in a particular field, and use SD to help you do your work better. In other words, you start with knowledge of a specialism other than SD, and that's what you offer to clients first. Then when they ask how come you did such a good job, you can explain all about SD.

John Swanson
Associate
Steer Davies Gleave
28-32 Upper Ground, London SE1 9PD
e. John.Swanson@sdgworld.net
w. www.steerdaviesgleave.com
Posted by ""Swanson, John"" <John.Swanson@sdgworld.net>
posting date Wed, 21 Dec 2005 13:37:34 -0000

Monte Kietpawpan kietpawpan yaho
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by Monte Kietpawpan kietpawpan yaho » Thu Dec 22, 2005 12:04 pm

Posted by Monte Kietpawpan <kietpawpan@yahoo.com>
Dear all,

SD and others are tools for decision making, just like religions
are means for doing good. Life is too short to master many
modeling paradigms. Genious Norbert Weiner studied Buddhism
but didn't understand it as correctly as he understand his religion.
Albert Einstein played Go (http://www.usgo.org), but perhaps
I and many Japanese boys do it better than he did.

As a system dynamicist, a useful thing to do is to
understand the true nature of this paradigm--SD, not of others--
other modeling approaches. That is why Donella Meadows
encouraged the SD community to search for a priori in SD paradigm.
If we want SD a popular method, let's not compare it with other approaches
because there might be balacing forces from people helding other paradigms.
Let's keep SD approach simple, not complicate it for academic.
Simplicity is a nature of SD approach that attracks me,
an SD beginner with SD books as teachers.

Best wishes,
Monte Kietpawpan


Monte Kietpawpan,
Ph.D. Program in Environmental Management,
Prince of Songkhla University,
P.O. Box 50 Ko Hong, Hat Yai, Songkhla 90112, Thailand
Posted by Monte Kietpawpan <kietpawpan@yahoo.com>
posting date Wed, 21 Dec 2005 23:28:44 -0800 (PST)

geoff coyle geoff.coyle btintern
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by geoff coyle geoff.coyle btintern » Fri Dec 23, 2005 12:33 pm

Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
John is absolutely spot on about the vital importance of really knowing about a domain, but that still leaves a difficulty. On a purely personal note, I hope that I have some knowledge, both theoretical and practical, about the mining industry and about defence, in both of which SD has powerful applications. However, if I restricted myself only to issues in those domains which can be addressed by SD I should look foolish, even obsessive, and I would miss out on all sorts of other interesting issues. Thus, I have to know that DES is the most appropriate tool for some very important types of defence problem, but that activity cycle simulation is better for others. Similarly, linear programming can handle production planning in some types of coal mine, but dynamic programming (which is not dynamic in our sense) is more suitable for some types of metal mining.

I don't necessarily have to know how to use all these tools, but I have to know that they exist, what they do, and what their advantages and limitations are. I suppose that this amounts to saying that I have to know when NOT to use SD.

Regards,

Geoff

Visiting Professor of Strategic Analysis,
University of Bath
Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
posting date Fri, 23 Dec 2005 10:41:03 -0000

geoff coyle geoff.coyle btintern
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by geoff coyle geoff.coyle btintern » Fri Dec 23, 2005 12:34 pm

Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
Bill,

I think that you are broadly right, though you still imply that the task is to 'sell' SD. Of course, it is a wonderful method when properly used for suitable issues but the mistake, maybe, is to call ourselves System Dynamicists (I NEVER do that) with the implication that we only do SD. That can come across to other analysts as 'SD is the only thing worth doing', which is patronising, offensive, and manifestly untrue.

Your key phrase is 'what if we listened and sold excellence in problem solving'. The corollary of that is that one might, for instance, say 'Sorry, SD, which is what I know about, won't tackle this problem, but DES might'. I like to think that I know about SD, but I'd be embarrassed to say that I didn't know anything about DES, linear programming etc. (If you want to see something different, have a look at my website.)

How about this for a bit of pre-Christmas unorthodoxy: maybe it was a mistake to found the SD Society, to which I must plead guilty as I helped to do it. Perhaps we should just be members of the OR Society, Institute of Management Sciences, etc and show ourselves as analysts who just happen to have a particular interest in SD, in parallel with other peers whose focus is on queuing theory, or whatever.

I think that I'd better sign off from this correspondence but I hope that you all have a Happy Christmas and an entertaining 2006.

Regards,

Geoff

Visiting Professor of Strategic Analysis,
University of Bath
Posted by ""geoff coyle"" <geoff.coyle@btinternet.com>
posting date Thu, 22 Dec 2005 18:11:18 -0000

John W. Rodat jwr signalhealth.c
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

SD and other modelling approaches

Post by John W. Rodat jwr signalhealth.c » Fri Dec 23, 2005 12:38 pm

Posted by ""John W. Rodat"" <jwr@signalhealth.com>
A couple of quick thoughts ...

Regarding Geoff Coyle's comment:

> Firstly, we must ask why the much larger OR/management science community > (some tens of thousands of people worldwide) does not see SD as a useful > methodology on a professional par with mathematical programming, queuing

This very much reminds me of the old Windows/Mac debate. One of the reasons that the more complex (Windows) platform ""won"" was precisely because it was more complicated and required the expertise of a ""priesthood."" The techies pretty consistently recommended the platform that required more of their service. (You can all visualize that causal loop, I'm sure.)

Re John Swanson's comment:

> I've long thought that trying to sell a technique like
> SD without focusing on an area of application can look quite weak to > potential clients. You risk looking naive, or that you are offering a

I strongly agree with John's point. That's one of the things that's exciting about special interest groups such as that for health care. Personally, I was in healthcare long before SD. Now when working on a healthcare issue, I always think in SD terms but may or may not tell my client. Though I usually try to at least sneak in a causal loop or very simple stock/flow somewhere in the conversation, when I do talk in SD terms, I vary the amount based on the client's outlook, patience, and, most importantly, openness to learning.

Happy New Year to all.

John W. Rodat
President
SignalHealth, LLC
Information Based Healthcare Strategies
Posted by ""John W. Rodat"" <jwr@signalhealth.com>
posting date Thu, 22 Dec 2005 10:25:40 -0500

Locked