[extropy-chat] System dynamics (Urban dynamics)

Anders Sandberg asa at nada.kth.se
Wed Jan 17 10:28:42 UTC 2007

Keith Henson wrote:
> "The model was, and is, very controversial, because it illustrates why
> many
> well-known urban policies are either ineffective or make urban problems
> worse. Further, the model shows that counter-intuitive policies -- i.e.,
> policies that appear at first glance to be incorrect, often yield
> startlingly effective results. As an example, in the Urban Dynamics model,
> a policy of building low income housing creates a poverty trap that helps
> to stagnate a city, while a policy of tearing down low income housing
> creates jobs and a rising standard of living for all of the city's
> inhabitants."

We might get a test of this in Beijing, as large parts of low income
housing in the city were torn down for the olympic city.

> I might add that system dynamics has a lot of ad hoc assumptions in the
> models.  Most of them are reasonable ones, such as economics, birth rated
> integrating to population levels and the like.

To me it looks a lot like a model where all plausible variables and
interactions are included, but the functional form of the interactions are
empirically unknown and hence have to be approximated by even more
plausible stuff. And if there is anything we have learned from dynamical
systems and computational biology it is that they matter tremendously. The
"counterintuitive dynamics" Forrester describes in
seems to be fairly typical instability, but he cannot determine what
causes it because the model is complex and somewhat arbitrary.

That is why I love zero-parameter models. Too bad they are very hard to
make :-)

> But now that Anders got me to thinking about this, system dynamics lacks a
> foundation to the level of biology.
> Another application for evolutionary psychology!

I think one need to model agents in this kind of system, both individual
humans but also the "agents" of parts of the cities. Many continous models
give a far too smooth behavior and don't show creative emergence in the
same way as when agents can select strategies and copy variants from each

Anders Sandberg,
Oxford Uehiro Centre for Practical Ethics
Philosophy Faculty of Oxford University

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