Ventana software support forum

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...

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...

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...

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) ...

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...

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 _________________...

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...

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 ...

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...

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 ...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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 ...

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...

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...

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 ...