From: Henry Baker <hbaker1@pipeline.com>

I think that this entire area

You mean the entire "complex systems" area rather than cybernetics, right?

has been subsumed by fractals, basins of attraction, etc.

About cybernetics, this page http://en.wikipedia.org/wiki/Control_theory has lots of subtopics and a history overview from before Maxwell thru after Weiner. I.e. it seems to be both thriving and hard core. By the way I didn't mean to say that human-design or analysis of hierarchical control systems was a dead end, only that it didn't lead to to the grand unifying paradigm for biological, psychological, social and engineered systems that some hoped it would.

Most of the folks in economics aren't aware of how chaotic complex systems can become, and they naively continue thinking that these systems can be "controlled"/"regulated". If we would only "regulate" the economy, we could somehow avoid the chaos.

I think chaos ideas are a clear fit in classical economics. I'm agnostic about what most economists know.

From: Dan Asimov <dasimov@earthlink.net>

The control theory I'm aware of is quite specific: It addresses the problem of how to steer most efficiently from one point to another in some phase space -- assumed locally Euclidean -- when the allowable steering options are subject to infinitesimal constraints. (Example: How do you best roll a sphere on a plane without slippage so its net motion is some prescribed rotation plus translation? Here "best" is defined by minimizing some cost function defined on all allowable itineraries.)

More generally: maintain some relationship between goal inputs and the current state given your sensors and actuators and other limitations and prejudices up to the designer. As I said, the wikipedia page gives an idea of the variety, from thermostats to inverse kinematics to AI.

Don't know much economics. Are there standard economics models as "multilayered feedback systems" ?

It's important to distinguish what economies do from what we can model about them. Good economists know in a common-sense way that economies are multi-level (for instance, a corporation has employees, managers and stockholders), but I'm not aware of any useful models that have that same character themselves. I guess economics overlaps science and kookery.

Despite having done research in differential dynamical systems, I never really understood what the field of "Complex Systems" or for that matter "Chaos Theory" were (and extend my skepticism to those fields as well).

At least notions like chaotic and "strongly mixing" have precise definitions with scientific (will the solar system eventually eject a planet?) and engineering ("divide and concur" algorithms) applications.

<< The funny thing is, hierarchical feedback systems are making a comeback with people like Jeff Hawkins, only it turns out every little piece of knowledge is its own feedback loop,

...

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How so?

Just in the technicalities of Hawkins' (synthesizing others') ideas. Everything's a minicolumn that has learned to do something in the process of two-way interactions up and down the cortical hierarchy.

I like the idea of hierarchical feedback systems (though maybe they can always be relabeled so as to be non-hierarchical?).

Right, the distinction between a system in which hierarchy tends to build up, and one that somebody designed or analyzed in a layered picture.

In any case they're probably useful in a field I'd love to see more progress in -- causal inference.

Like/not like Jeff Hawkins (_On Intelligence_ and Numenta)? --Steve