Ventana software support forum

The Beer Game has always intrigued me. Typically it produces explosive oscillation due to the use of simple proportional control and the presence of delays. A real brewery does not oscillate explosively and would go bankrupt if it did. The Beer Game has no real-world equivalent and the lessons it te...

Id really be careful about making the model more detailed as a substitute for making it smart. In my philosophy of SD (borne out by a certain amount of experience) there are sophisticated models and there are large models but there are no large sophisticated models. World Dynamics is only about 100 ...

Kim Warren is right, if you cant get reliable structure AND numbers then simulation is dangerous. The outputs from the model will be unreliable and hence the conclusions drawn from them might be misleading or wrong. the same is true when dimensional analysis is ignored. Regards, Geoff geoff.coyle@bt...

Ivan, This is a very interesting topic and an exceedingly important one (Ive worked on defence problems using SD for years and this is a crucial issue). Put too simply, the crux of the matter is what sort of balance of investment helps commanders (and their staffs) to win wars. Information overload ...

Theres a diagrammatic model of psychogeriatric health care in a paper of mine in the next issue of System Dynamics Review. I hope that helps but please get in touch if you need any more info. Come to think of it, please give me a call in any case as Im always keen to meet new SD people in the UK (RE...

Yes, Ive built loads of models using stochastic effects. One is to do with coal production (Journal of the Operational Research Society, Vol. 36, No. 4, pp 307-318, 1985 and Vol. 42. No. 6, pp 435-462, 1991). See also my book System Dynamics Modelling CRC Press, 1996 for a full discussion of the cor...

Dear SD Community, I want to draw your attention to the Fourth UK SD Gathering. These are annual events sponsored by the UK Chapter of the SD Society and bringing together the UK SD community for a discussion and social event. It is not necessary to be British to attend this meeting, though it may d...

Folks,

A few weeks ago I asked for information on the teaching of SD. So many of
you have replied that I juts cannot thank you all individually as I normally
would. Please accept this as a blanket thank you.

Geoff
From: "Geoff Coyle" <Geoff.Coyle@btinternet.com>

Folks, Now that I am somewhat retired, though I certainly could not find the time to go back to work, I have it in mind to do some research, perhaps as a survey paper, on the teaching of SD around the world. Before I can frame my hypothesis (sounds good, if only I knew what it meant) I need to find ...

There was a full issue of System Dynamics Review which dealt with health
care.

Geoff Coyle
Geoff.Coyle@btinternet.com

Ivo,

Good to know you still exist. Theres a chunk on police effectiveness in my
book.

Geoff
From: "Geoff Coyle" <Geoff.Coyle@btinternet.com>

>using soft data in business modelling. >apart from marketig our presently restricted experience is: use hard data >and models only and treat soft arguments in negociating with the hard >simulated evidence. This is absolutely the right advice. By persisting in quantifying what cannot be quantified w...

Jim Hines wrote: > Geoff Coyles formula N=DEL^2/Vn is very nice and I for one agree that I > should have read his book a long time ago. > That was very kind. Can I claim that this be now known as Coyles Law? Apart from the echo phenomenon, DELAY3 is usually perfectly satisfactory for the poor qualit...

Kym Warren and Bruce Campbell make some interesting points in this discussion of the two-analyst problem - two equivalent people should come up with something like the same model given the same information. Ideally that should be the case though we need to remember that even eminent surgeons dont pr...

Mr Mooy, I think you are on the wrong track in trying to get an existing model or part of one to plug into your problem. There are two reasons which are absolutely fundamental in any modelling, not just SD. The first is that a model is always developed for a purpose (or it should be) such as to answ...

This is an old and interesting problem. My 1977 book Management System Dynamics, John Wiley (long out of print but should be available in any serious SD library) has 4 pages on measuring the order of a delay. The end result is: N=DEL^2/Vn where N is the required delay order, DEL is the delay magnitu...

I absolutely agree with Jims point that educating the client is a VITAL part of practical consultancy. Yes, I like to get paid but I like it even better when I feel that I have done a satisfying job. An uneducated client who can be bemused by superfluous detail and bedazzled by a smart and playful G...

This is, in fact, a VERY tricky problem. Simply citing textbooks (even mine, which I am sure you must know about in any case) doesnt help you. (I HOPE that you have at least read the books and are not just relying on a software manual!!). As Bill Harris said, whats the problem youre trying to model?...

This correspondence gets more interesting by the day. I bow to Keiths practical experience in government work though it has not been the same as mine. Usually, the people I work with are not too interested in the 49 year olds as opposed to the 50s, 51s and so on. They want to talk about the middle-a...

THIS NOTE IS FOR ALL MEMBERS OF THE SD SOCIETY LIVING IN THE UNITED KINGDOM. The formation of the UK Chapter of the Society was approved by the Policy Council of the System Dynamics Society Inc. during 1999. The Chapter will hold its first annual meeting on February 3/4 in Harrogate, previous meetin...

Keith Linards note about the use of census data shows the value of this discussion forum as it has made me think a bit more deeply about the use of numerical data in SD models. One aspect is the cleverness of being able to make Excel talk to Powersim, or whatever, but the other is the underlying ass...

I havent understood what all this debate was about. Surely, this is all just BASIC STUFF in SD. Rod Browns answer is exactly right. Regards, Geoff geoff.coyle@btinternet.com Professor Geoff Coyle Consultant in System Dynamics and Strategic Analysis Tel: (44) 01793 782817 Fax: 01793 783188 ----- Orig...

My good friend Keith Linard makes some interesting points about using arrays to model census-based population data but, equally, his reply raises some questions in my mind. Lets look, first, at the hidden assumptions in such an apparently precise model with 100 age categories and 2 sexes. One is tha...

Dear All, A couple of weeks ago someone who shall be nameless sent my email address, without first asking my permission, to Ericcson Telephone in the hope of getting a free mobile phone. The invitation from Ericcson wasa hoax and, unhappily, also contained a virus which infected my signature file. W...

Keith, Yes, it is very worthwhile as a caution against what Im increasingly seeing as the risk of recklessness in modelling. Another VERY valuable source is two papers by Wes Churchman on the false assumptions in operational research. They were originally in Journal of the Operational Research Socie...