[Martin Taylor 931221 17:30]
(Rick Marken 931221.1330)
So, is the bottom line that there is no simple, straight- forward
way to describe a non-controlling negative feedback organization?
No. There is no simple straightforward way to make a quantitative
demonstration in a self-organized structure that I can think of at
the moment, and since such structures inherently demand a non-linear
effect somewhere along the line, all the problems of nonlinear
mathematics are likely to show up in any such system.
I have already done what you say is not doable, to DESCRIBE the system.
Bill P wants numbers, and I'd love him to get them, not least because
I would then be more (or less) sure that my analysis was right.
I thought you were trying to show that a variable reference signal
is essential for control (purpose).
How could you still think that, after my MANY times having pointed out
that what I was looking for was an agreement on word usage. Is the
purpose of a control system to bring its perceptual signal to its
reference level? If so, there'd better be a reference level for it
to bring it to. If there's a signal for the reference level, what's
the point of it unless it can vary? Everyone knows that a negative
feedback loop will bring SOMETHING to a relatively stable value. My
original question is whether people wanted to use the words "purpose"
and "control" to refer to all such SOMETHINGs. My preference is to
use it for negative feedback systems that bring and keep a perceptual
signal near a reference level that is an input to the system. But for
the sake of better communication, I'll use the words however the majority
prefer.
I guess, now, that I am going
to have to take the existence of such systems on faith because,
apparently, the only examples of non-controlling negative feedback
systems (of the MANY that you say exist in nature) are non-linear
systems that are as complex as the vortex.
Faith, it's wonderful.
You can't get very far away from self-organized structures in far from
equilibrium energy flows (apart from being one yourself). But that doesn't
make it easy to seek out one that is easily analyzed and has visibly
lumped components and has not evolved into a hierarchic (purposeful by
any way of useing the word) control system.
I have been unable to make heads or tails of the vortex conversation
(I lost it when the vortex changed from a negative to a positive
feedback system).
If you think it changed, you didn't read much of the earlier postings
on the topic. That was pretty up front. Though I must admit, Tom missed
it, too, which is not like him. So I guess I didn't emphasize it, thinking
it obvious initially.
I guess I'll never understand what the dynamical
systems approach can contribute to my understanding of living systems.
Sigh. I believe you are correct. But you can keep trying if you choose.
ยทยทยท
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Changing the topic, Dag has compiled an IBM PC set of demos. How about
you compiling a set of whatever demos and utilities might be available for
the Mac? Since you have written many of them, I think you are the logical
person to do it. I'll send you an up to date version of the Control
Builder, that we do not intend to upgrade for quite some time now, although
it still carries a "beta" designation. It includes all Bill P's Primer
examples through volume 3, plus a couple of more complex examples.
Martin