Search found 25 matches

by Tom Fiddaman <tom@ventanasyst
Mon Dec 08, 2008 7:15 am
Forum: SD Mailing List Archive
Topic: ANNOUNCE PCT and an economic emergency
Replies: 9
Views: 16168

ANNOUNCE PCT and an economic emergency

Posted by Tom Fiddaman <tom@ventanasystems.com> John Voyer correctly notes that positive feedbacks in the economy are not news. The multiplier-accelerator and other theories have been around for a long time. Where Powers really goes astray is with the notion that we can build a model, reach consensu...
by Tom Fiddaman <tom@ventanasyst
Thu Jul 17, 2008 7:13 am
Forum: SD Mailing List Archive
Topic: QUERY Wikis and public perception
Replies: 1
Views: 3412

QUERY Wikis and public perception

Posted by Tom Fiddaman <tom@ventanasystems.com> The comments Ralf cites sound to me like the actions of an overzealous editor with limited knowledge of SD and a strangely narrow conception of wikis. There's probably not much value in getting into a flame war with such an individual, who might be har...
by Tom Fiddaman <tom@ventanasyst
Tue May 20, 2008 6:47 am
Forum: SD Mailing List Archive
Topic: QUERY Models, Problems and Systems
Replies: 29
Views: 79916

QUERY Models, Problems and Systems

Posted by Tom Fiddaman <tom@ventanasystems.com> At 06:18 AM 5/15/2008, SDMAIL Christina Spencer wrote: > I agree that it is perfectly reasonable that people with questions that > may have come up before should investigate before posting old questions > - but how are they supposed to do that? One sou...
by Tom Fiddaman <tom@ventanasyst
Sat May 10, 2008 6:54 am
Forum: SD Mailing List Archive
Topic: QUERY Limits to Growth Plan B
Replies: 26
Views: 26355

QUERY Limits to Growth Plan B

Posted by Tom Fiddaman <tom@ventanasystems.com> Jack and others have noted that managing the globe involves two subproblems: 1. figuring out the problem (e.g., are there limits, what are they, when do they become binding) 2. convincing others to act (hard when others may be uninformed or predatory) ...
by Tom Fiddaman <tom@ventanasyst
Fri Apr 25, 2008 6:34 am
Forum: SD Mailing List Archive
Topic: QUERY Meaning of Stock/Level
Replies: 46
Views: 36564

QUERY Meaning of Stock/Level

Posted by Tom Fiddaman <tom@ventanasystems.com> I think Jack's latest missive has clarified the debate: > So again, it appears we have these two premises: > 1. ""any variable that can change only over time, needs to be treated as > a stock."" > 2. ""Temperature cannot c...
by Tom Fiddaman <tom@ventanasyst
Tue Apr 22, 2008 7:23 am
Forum: SD Mailing List Archive
Topic: QUERY Definition of exogenous
Replies: 5
Views: 7253

QUERY Definition of exogenous

Posted by Tom Fiddaman <tom@ventanasystems.com> A replication of the Market Growth model that John Morecroft cited is in my model library at http://metasd.com/models/index.html#Business Tom Posted by Tom Fiddaman <tom@ventanasystems.com> posting date Mon, 21 Apr 2008 15:58:18 -0600 _________________...
by Tom Fiddaman <tom@ventanasyst
Tue Apr 22, 2008 7:23 am
Forum: SD Mailing List Archive
Topic: QUERY Who wants to share models
Replies: 24
Views: 23018

QUERY Who wants to share models

Posted by Tom Fiddaman <tom@ventanasystems.com> Mabel Fong raises a good point: > First, is it not a general commonplace of complex non-linear > dynamic systems analysis that one does not even claim to have a model > until it > has produced the same stimulus/response behaviors when programmed in > d...
by Tom Fiddaman <tom@ventanasyst
Sat Apr 12, 2008 7:06 am
Forum: SD Mailing List Archive
Topic: QUERY Meaning of Stock/Level
Replies: 46
Views: 36564

QUERY Meaning of Stock/Level

Posted by Tom Fiddaman <tom@ventanasystems.com> At 10:40 PM 4/9/2008, Alan McLucas wrote: > I am yet to be convinced that representations of soft variables that > often appear in SD models are routinely and comprehensively validated, > rather than just appearing to be plausible. I would dearly love ...
by Tom Fiddaman <tom@ventanasyst
Thu Apr 10, 2008 7:23 am
Forum: SD Mailing List Archive
Topic: QUERY Meaning of Stock/Level
Replies: 46
Views: 36564

QUERY Meaning of Stock/Level

Posted by Tom Fiddaman <tom@ventanasystems.com> At 05:59 AM 4/9/2008, SDMAIL Alan McLucas wrote: > Stocks in system dynamics models represent quantities of material. The > stock-and-flow representation has precise and unambiguous meaning: > stocks accumulate or integrate their flows; the net flow in...
by Tom Fiddaman <tom@ventanasyst
Wed Apr 09, 2008 7:59 am
Forum: SD Mailing List Archive
Topic: QUERY Who wants to share models
Replies: 24
Views: 23018

QUERY Who wants to share models

Posted by Tom Fiddaman <tom@ventanasystems.com> Posted by ""'richard dudley'"" <richard.dudley@attglobal.net> > Modelwiki looks like a good experiment for sharing models (as opposed to > the related question of collaborative model building). Right. One could certainly use a wiki ...
by Tom Fiddaman <tom@ventanasyst
Sat Apr 05, 2008 6:22 am
Forum: SD Mailing List Archive
Topic: QUERY Who wants to share models
Replies: 24
Views: 23018

QUERY Who wants to share models

Posted by Tom Fiddaman <tom@ventanasystems.com> At 04:31 AM 4/4/2008, SDMAIL Bobby Powers wrote: > I think what we need is something similar for modelers: a free service > that allows you to quickly add a site for your model, upload it, link to > or upload related publications, and perhaps have a sm...
by Tom Fiddaman <tom@ventanasyst
Thu Mar 13, 2008 6:57 am
Forum: SD Mailing List Archive
Topic: QUERY Open Source Simulation Software for SD
Replies: 22
Views: 22221

QUERY Open Source Simulation Software for SD

Posted by Tom Fiddaman <tom@ventanasystems.com> I'm not convinced that competition is the obstacle to SMILE/XMILE implementation. That presumes that SD software providers have a strong incentive to restrict access to a valuable network or installed base of models, or that they behave like the teleco...
by Tom Fiddaman <tom@ventanasyst
Tue Nov 13, 2007 8:39 am
Forum: SD Mailing List Archive
Topic: QUERY Ensuring Quality of Models
Replies: 13
Views: 15092

QUERY Ensuring Quality of Models

Posted by Tom Fiddaman <tom@ventanasystems.com> > Ultimately, the ONLY fundamental criterion of SD model validity is ""what > did it change, in what direction, and by how much?"" I'd call this influence, not validity. A completely spurious model could be involved in a process tha...
by Tom Fiddaman <tom@ventanasyst
Sun Oct 14, 2007 7:49 am
Forum: SD Mailing List Archive
Topic: QUERY Structural changes and validity
Replies: 17
Views: 12218

QUERY Structural changes and validity

Posted by Tom Fiddaman <tom@ventanasystems.com> >No existing validity tests serve to check whether the relationships in the real system >will not significantly change in the future--within the time horizon. I don't believe that this is strictly true. For example, as a matter of habit I include a fir...
by Tom Fiddaman <tom@ventanasyst
Sun Oct 14, 2007 7:49 am
Forum: SD Mailing List Archive
Topic: QUERY Structural changes and validity
Replies: 17
Views: 12218

QUERY Structural changes and validity

Posted by Tom Fiddaman <tom@ventanasystems.com> >No existing validity tests serve to check whether the relationships in the real system >will not significantly change in the future--within the time horizon. I don't believe that this is strictly true. For example, as a matter of habit I include a fir...
by Tom Fiddaman <tom@ventanasyst
Thu Sep 13, 2007 1:24 pm
Forum: SD Mailing List Archive
Topic: QUERY Why don't organizations function better?
Replies: 21
Views: 13409

QUERY Why don't organizations function better?

Posted by Tom Fiddaman <tom@ventanasystems.com> I agree that an organization depends on its employees, but it doesn't follow that the employees are dependable. Outside a firm, markets provide some discipline - many inducement-contribution pairs are easy to verify because there are prices and enforce...
by Tom Fiddaman <tom@ventanasyst
Wed Sep 12, 2007 1:00 pm
Forum: SD Mailing List Archive
Topic: QUERY Why don't organizations function better?
Replies: 21
Views: 13409

QUERY Why don't organizations function better?

Posted by Tom Fiddaman <tom@ventanasystems.com> The conversation seems to have turned to an explanation of organizational performance that doesn't leave much room for the visionary warrior-strategist CEO. Does that say more about the world, or about our world view? It seems to me that the key evolut...
by Tom Fiddaman <tom@ventanasyst
Tue Sep 11, 2007 1:05 pm
Forum: SD Mailing List Archive
Topic: QUERY How to promote good work
Replies: 26
Views: 22038

QUERY How to promote good work

Posted by Tom Fiddaman <tom@ventanasystems.com> A few more wishes for discussion 2.0 expressed: In addition to: > - input from email-only users > - high discussion quality > - civility > - email distribution and digests > - more open discussions > - distribute moderation burden more widely > - searc...
by Tom Fiddaman <tom@ventanasyst
Fri Sep 07, 2007 6:29 pm
Forum: SD Mailing List Archive
Topic: QUERY How to promote good work
Replies: 26
Views: 22038

QUERY How to promote good work

Posted by Tom Fiddaman <tom@ventanasystems.com> It seems to me that improving electronic support for collaboration is a two step process: decide what we want, then find & implement software to do it. For discussion (i.e. a possible successor to this list), there have been a number of wants expre...
by Tom Fiddaman <tom@ventanasyst
Wed Sep 05, 2007 1:50 pm
Forum: SD Mailing List Archive
Topic: QUERY How to promote good work
Replies: 26
Views: 22038

QUERY How to promote good work (SD6555)

Posted by Tom Fiddaman <tom@ventanasystems.com> I wish that Richard's second post (SD6568) had arrived first, because it contained constructive ideas that I was not able to retrieve from memory upon reading the first (SD6555). Some of those ideas have extremely low cost and could be implemented righ...
by Tom Fiddaman <tom@ventanasyst
Sun Apr 22, 2007 3:31 am
Forum: SD Mailing List Archive
Topic: QUERY Age of material in a stock
Replies: 28
Views: 25867

QUERY Age of material in a stock

Posted by Tom Fiddaman <tom@ventanasystems.com> Pardon me while I dodge Jay's question and pursue the technical details a little further. Richard Dudley and I wondered if Jack Homer's arrival-time-coflow structure (ATCS) was equivalent to my time-integrating-coflow structure (TICS). Richard got moti...
by Tom Fiddaman <tom@ventanasyst
Thu Apr 19, 2007 1:06 pm
Forum: SD Mailing List Archive
Topic: QUERY Age of material in a stock
Replies: 28
Views: 25867

QUERY Age of material in a stock

Posted by Tom Fiddaman <tom@ventanasystems.com> It's worth noting a few consequences of Jack's analysis: - The fractional growth rate G is only constant for exponential growth or decay. Growth in the stock leading to As<To means the average age of material is younger than you'd expect from Little's ...
by Tom Fiddaman <tom@ventanasyst
Tue Apr 17, 2007 12:39 pm
Forum: SD Mailing List Archive
Topic: QUERY Age of material in a stock
Replies: 28
Views: 25867

QUERY Age of material in a stock

Posted by Tom Fiddaman <tom@ventanasystems.com> Another coflow approach: There's no general rule that applies for all inputs. One possibility is to add a coflow to the model to track time spent in the stock. This is implemented the way you'd track average experience of staff in a workforce model. In...
by Tom Fiddaman <tom@ventanasyst
Tue Feb 06, 2007 3:12 pm
Forum: SD Mailing List Archive
Topic: QUERY Climate change
Replies: 10
Views: 7713

QUERY Climate change

Posted by Tom Fiddaman <tom@ventanasystems.com> David Corben is puzzled at the SD community's apparent affection for climate models. As far as I know the SD community has little direct involvement with physical models of climate, and is mainly concerned with the policy implications of the physics gi...
by Tom Fiddaman <tom@ventanasyst
Fri Feb 02, 2007 2:31 pm
Forum: SD Mailing List Archive
Topic: QUERY The Death of System Dynamics?
Replies: 26
Views: 30340

QUERY The Death of System Dynamics?

Posted by Tom Fiddaman <tom@ventanasystems.com> I'm sympathetic to Richard Stevenson's worries about the field. However, I'm unsure e xactly what his prescription is. ""Get back to roots"" doesn't seem like enough. Was SD growing much faster in the Industrial Dynamics days? Does ...