Ventana software support forum

Posted by Tom Fiddaman <tom@vensim.com> >In Jim Hines' workshop at ISDC >2005 in Boston there was brief discussion of<br> >the MIN and MAX function and their use in preventing a stock from going >negative (where such a thing could not happen in reality, such as >potential customers). The point, as I...

Posted by Tom Fiddaman <tom@vensim.com> Generically, if you can't reproduce your data with consistent parameter values, there is something wrong (or perhaps just missing) in your model. It's hard to say more without getting into specifics of the model, but I think the key question is *why* a1 has to...

Posted by Tom Fiddaman <tom@vensim.com> I usually hear this expressed as ""all models are wrong; some models are useful."" I must confess that I've grown a little wary of this statement, though not because it's bad marketing. Instead, I've heard it used as an excuse for mediocre ...

Posted by Tom Fiddaman <tom@vensim.com> I think everyone's right here, but the fuzzy language distinction between the fractional growth rate of a stock and the absolute rate of change of a stock is making it hard to see. In Barry's argument, it's the former that matters, because the important thing ...

Posted by Tom Fiddaman <tom@vensim.com> A model without feedback loops is to System Dynamics what warming up a TV dinner in the microwave is to gourmet cooking. Sometimes it might be useful and the right thing to do, but it's a different beast. >Kim Warren's Forrester Award presentation reiterated t...

Posted by Tom Fiddaman This is not at all a naive question - there are so many dimensions to the answer I hardly know where to begin or end. Nevertheless I'm always game for a good ramble, so here goes. First comes the question of "growth of what?" Usually this means GDP, but that just con...

Posted by Tom Fiddaman <tom@vensim.com> >>Posted by George A Simpson <gsimpso4@csc.com> >> >>I didn't see the points about ""Limits to Growth"" as an implied criticism of >>the field at all. I think the reason the comments about LTG struck a nerve is that there have been so many ...

Posted by Tom Fiddaman <tom@vensim.com> WAS Problem Solving versus Optimization (SD5227) There's also a copy of the Wonderland model in my model library. It's the 7th item down at: http://www.sd3.info/models/index.html#Climate It's a replication based on the original publication about the model: Ale...

Posted by Tom Fiddaman <tom@vensim.com> WAS Problem Solving versus Optimization (SD5226) Jack Homer wrote: >>Many ridiculous things have been said about LTG/SD, and this adds to that >>list. But because the article is in a magazine with large circulation and >>seems so dishonest and self-serving, I'...