Search found 94 matches

by "geoff coyle"
Sun Jan 18, 2004 10:52 am
Forum: SD Mailing List Archive
Topic: Qualitative SD for Oxford
Replies: 0
Views: 2535

Qualitative SD for Oxford

Folks, Some time ago I put out an announcement of a stream of qualitative SD for Oxford. That has produced a good deal of reaction and we are well on the way to a very successful stream covering a wide variety of issues. You were asked to send abstracts to me, and its still not too late to submit yo...
by "geoff coyle"
Mon Jan 12, 2004 11:47 am
Forum: SD Mailing List Archive
Topic: Can SD models be validated without being run?
Replies: 38
Views: 27356

Can SD models be validated without being run?

Yaman RIGHTLY reminds us of what, and Jay Forrester pointed this out well over 40 years ago, is the fundamental test - that the models defence rests on justifying its equations, not on its comparison to observed data. To be sure (and this was not Kims original question) it is comforting if the simul...
by "geoff coyle"
Fri Jan 02, 2004 6:05 pm
Forum: SD Mailing List Archive
Topic: new book on strategic analysis
Replies: 0
Views: 2763

new book on strategic analysis

Dear SD colleagues and friends, I am pleased to tell you that my new book, Practical Strategy: Structured Tools and Techniques, was published by Pearson Education in November 2003. Unlike my previous work, this book has very little about SD so why should you be interested? The reason is that the boo...
by "geoff coyle"
Mon Dec 29, 2003 10:59 am
Forum: SD Mailing List Archive
Topic: New stream for Oxford 2004
Replies: 0
Views: 5048

New stream for Oxford 2004

The growth in qualitative system dynamics, QSD, in which only a diagram is built and there is no simulation, has been considerable over the years. In particular recent work on the use of structural analysis to replace detailed, simulation-based dynamic investigation has shown how powerful this is fo...
by "geoff coyle"
Wed Dec 03, 2003 11:31 am
Forum: SD Mailing List Archive
Topic: Discrete vs. continuous (or aggregated) representation
Replies: 1
Views: 7005

Discrete vs. continuous (or aggregated) representation

As usual, Jay has hit the nail on the head. Whether one uses one simulation paradigm or another depends on the nature of the problem, the purpose of the analysis and, perhaps above all, on the nature of the question to be answered. I tried to make the same points in my earlier email about distributi...
by "geoff coyle"
Fri Nov 21, 2003 10:01 am
Forum: SD Mailing List Archive
Topic: Discrete Event vs. DiffEq Models
Replies: 4
Views: 12370

Discrete Event vs. DiffEq Models

1 This is a common class of problem that arises in many domains - the workload in a machine shop is but one of many cases. It is usually addressed, as you have done, by discrete event simulation (DES) using any one of a number of DES languages. (CSL was a good one but Im not sure what is now availab...
by "geoff coyle"
Fri Sep 05, 2003 9:24 am
Forum: SD Mailing List Archive
Topic: Evolution of Language?
Replies: 7
Views: 6039

Evolution of Language?

This sounds like a fascinating question but Id hate to rush into it without
finding out more about the domain knowledge. Can your friend point you to
what Id guess would be an extensive literature?

Geoff
From: "geoff coyle" <geoff.coyle@btinternet.com>
by "geoff coyle"
Sat Aug 02, 2003 10:04 am
Forum: SD Mailing List Archive
Topic: Where are we in the Long waves
Replies: 12
Views: 9641

Where are we in the Long waves

John rightly cites the volume of work on models (something that I mentioned in my first query). Its certainly an impressive collection, ranging over the last 20 years but it does not, as far as I can tell, address the issue of empirical evidence for the waves existence. Geoff From: "geoff coyle...
by "geoff coyle"
Fri Aug 01, 2003 9:28 am
Forum: SD Mailing List Archive
Topic: Where are we in the Long waves
Replies: 12
Views: 9641

Where are we in the Long waves

Brenda refers to the macroeconomic variables, but surely we also need to talk about long waves (if they exist) in more general social/political/technological variables. I do though, support her view that we need some kind of consensus on what a wave would have to include before we could start to loo...
by "geoff coyle"
Sat Jul 26, 2003 9:15 am
Forum: SD Mailing List Archive
Topic: Where are we in the Long waves
Replies: 12
Views: 9641

Where are we in the Long waves

Folks, This could well turn out to be a very interesting correspondence. Bill posed a fascinating question but could find only two mentions of Kondratieff on Google, suggesting that the long wave is not a big issue with economists. Jay (Forrest) is comfortable with back to basics. The trouble with t...
by "geoff coyle"
Tue Apr 30, 2002 10:11 am
Forum: SD Mailing List Archive
Topic: Models of regional conflicts and other queries
Replies: 0
Views: 2850

Models of regional conflicts and other queries

This kind of question is interesting but, all too often, the questioner does not make it clear why he/she wants to do what they are asking about. That makes it hard to send a sensible and helpful reply. Id urge people to be more precise. [ Hosts Note: Geoff is absolutely right. If you want to post a...
by "geoff coyle"
Sat Apr 27, 2002 2:19 pm
Forum: SD Mailing List Archive
Topic: Growth of mujahidin in Afghanistan and Baysian belief networ
Replies: 6
Views: 4969

Growth of mujahidin in Afghanistan and Baysian belief networ

Folks, This correspondence about the Rev Dr Thomas Bayes, the Mujahidin, and Afghanistan reminds me of the USS Maine (bear with me, there will be two points). Point 1 (a little light-hearted). The sinking of this battleship in Havana harbour, apparently as a result of a terrorist act, led to the Spa...
by "geoff coyle"
Fri Apr 26, 2002 9:52 am
Forum: SD Mailing List Archive
Topic: SD Models from Written Text
Replies: 30
Views: 28202

SD Models from Written Text

George makes a good point. One of the uses of expert systems is to archive the knowledge of skilled and experienced people. There is, as he says, a need for some really good research into how experienced modellers (and not only in SD) go about their business. How, then, do novices learn the same ski...
by "geoff coyle"
Thu Apr 25, 2002 9:27 am
Forum: SD Mailing List Archive
Topic: community health & evidence -a role for system dynamics?
Replies: 6
Views: 6328

community health & evidence -a role for system dynamics?

This strikes me as being a bit dodgy. Lets look at the park lighting first and imagine a scale from 0 to 1. So, 0 means no lighting at all, so thats clear (well, dark actually, at any rate at night). At the top end , 1 must mean perfect, but what does that actually mean? What is perfect to one perso...
by "geoff coyle"
Tue Apr 23, 2002 9:53 am
Forum: SD Mailing List Archive
Topic: Dimensional Consistency
Replies: 1
Views: 6068

Dimensional Consistency

Joel, I stand corrected! Well done, though I havent seen dimensions/units even mentioned in the index of any OR text (though I havent reviewed all of them). One re-order formula I know of, which is in regular use by a large organisation, is dimensionally invalid! When I pointed that out, they just l...
by "geoff coyle"
Sat Apr 20, 2002 9:56 am
Forum: SD Mailing List Archive
Topic: Economic Dynamics
Replies: 3
Views: 4032

Economic Dynamics

What an interesting problem. How does it fit with Baumols Economic Dynamics, or is that old hat? Id raise three issues: First, and maybe most important, what is the purpose of the model? What well-chosen questions is it designed to answer? Second, how have you ensured that it is dimensionally consis...
by "geoff coyle"
Fri Apr 19, 2002 9:40 am
Forum: SD Mailing List Archive
Topic: System Dynamcis work on terrrorism
Replies: 9
Views: 7227

System Dynamcis work on terrrorism

Bruce wrote: > > Next why do you feel like that it would be an inappropriate time for SD > work on terorism to be published? You are correct, everyone can read, but > do feel that the work currently being published (and read) on terrorism is > the most appropriate? Wouldnt now be an ideal time to of...
by "geoff coyle"
Fri Apr 19, 2002 9:28 am
Forum: SD Mailing List Archive
Topic: Using DT in Model Equations
Replies: 6
Views: 6418

Using DT in Model Equations

Jim, as usual, adds interesting ideas to a debate that seems to have got out of all proportion. > Also: Geoff, what are the three permissible uses of dt? Non-negativity, as discussed; introducing quantity via PULSE (depends on the s/w); resetting things such as accounts to zero at the end of a year ...
by "geoff coyle"
Wed Apr 17, 2002 10:26 am
Forum: SD Mailing List Archive
Topic: Negative Stocks
Replies: 4
Views: 8511

Negative Stocks

Raymond, Surely youd treat the stock as the quantity of water in the tanks (probably two separate stocks). The depth of water in a tank is then an auxiliary calculated from the quantity and the size of the tank. The head of water between the tanks is another auxiliary, representing the pressure diff...
by "geoff coyle"
Wed Apr 17, 2002 10:22 am
Forum: SD Mailing List Archive
Topic: Negative Stocks
Replies: 4
Views: 8511

Negative Stocks

Bill asks if treating negative stock explicitly as a backlog is a heuristic or a firm rule and refers to his financial problems (donations can be sent to me and Ill pass them on, less the usual commission). Id suggest that it depends on whether or not behaviour changes. Someone whose bank balance is...
by "geoff coyle"
Wed Apr 17, 2002 7:35 am
Forum: SD Mailing List Archive
Topic: Using DT in Model Equations
Replies: 6
Views: 6418

Using DT in Model Equations

Date: Wed, 17 Jul 2002 09:59:53 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Jim Hines says: > First is the question of where the word "widget" comes from. According > to the American Heritage Dictionary, the word "wi...
by "geoff coyle"
Sun Apr 14, 2002 12:14 pm
Forum: SD Mailing List Archive
Topic: Representing constraints
Replies: 30
Views: 43684

Representing constraints

Christopher is right, the use of /DT is only one way of representing a constraint. It corresponds to a policy of deliver until we run out of stock. An alternative is a policy of slow deliveries (or whatever) as we get closer to stock out. The latter would be better handled by a table function though...
by "geoff coyle"
Sat Apr 13, 2002 8:58 am
Forum: SD Mailing List Archive
Topic: System Dynamcis work on terrrorism
Replies: 9
Views: 7227

System Dynamcis work on terrrorism

Rod MacDonald asks: > I was wondering what information exists on the listserve about folks > undertaking modeling projects that deal with terrorism in any of its This is a subject on which work has been published, but some time ago. However, I am not at all sure that it would be a good idea to publi...
by "geoff coyle"
Fri Apr 12, 2002 9:18 am
Forum: SD Mailing List Archive
Topic: This List and The System Dynamics Society
Replies: 8
Views: 12944

This List and The System Dynamics Society

Jim makes some good and helpful points, and corrects my error that the list is society sponsored. Other respondents have misread my suggestion and reacted less sensibly. Of course, no one - least of all me - wants to limit discussion to Society members or to turn away enquiries. All I said was that ...
by "geoff coyle"
Wed Apr 10, 2002 10:26 am
Forum: SD Mailing List Archive
Topic: Representing constraints
Replies: 30
Views: 43684

Representing constraints

Not sure I really agree with Yaman. SD treats all entities as though they are physical quantities (even soft variables such as Consumer Satisfaction) and physical systems usually cannot have negative quantities (there are exceptions - a negative STOCK might be a backlog). So, if something that shoul...