NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/bit/listserv/csgl/1932

Text File | 1992-12-22 | 6.1 KB | 127 lines

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Date:         Mon, 21 Dec 1992 16:18:15 EST
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Subject:      Re: Martin to Rick on Shannon
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[Martin Taylor 921221 15:30]
(Tom Bourbon 921221  10:15)

>   Tom to Martin (in the present:
>All you need do in the case of coordination between two systems is
>show me how, working back from Shannon's principles, you end up
>with two interacting PCT systems, each with the features Bill
>postulated for a single system.  If the models that emerge from
>Shannon's principles are identical to those presently envisioned in
>PCT, your point is made.

Is that what you want?  I had misinterpreted you to mean that you wanted
numerical predictions that came from a different source but were as good
as your predictions.  I said that was an inappropriate challenge because
your model would be at least as good, coming as it does from a presumably
correct structure, as would a model of the same structure derived from an
information-theoretic background.

The challenge you now pose is worth trying.  And it might help shed some
light on the arguments that were going on a month or two ago between Bill
and Greg about social control.

=============
>    Martin replying to Bill Powers' reply to Martin's reply to Tom:
>(TB: What tangled webs we weave ...!

It happens when we get a discussion of more than two people.  But no-one here
is trying to deceive, as far as I can see.  If they are, it's pretty well
done...  I much prefer multi-party discussions to discussions by X + Bill P.
===============
>   Tom to Martin (in the present):
>Perhaps Bill and I both missed it, but I did not see where you used
>Shannon to demonstrate that neither S-R or Plan-then-execute models
>would be viable.  Your remark leads me to think that you also used
>Shannon to demonstrate that a PCT model would be viable.  Was that
>the case?

Yes.  And in trying your challenge, I suspect I will have to go over
that same ground again, so maybe I will be able to make it intelligible.

What I think I will have to do is to write what amounts to a serious
paper rather than a set of impromptu come-backs on-line.  I have not
seriously considered the two-person version in light of information
theory hitherto, so it will take a little thought to get it right.  I
was dealing only with why PCT was both necessary and (usually) sufficient
for a living organism.  ("Usually", because accidents can kill.)  Now
we must deal with another controller.  I don't know whether this will
change the analysis or not.

>I said that if you don't understand Shannon, you won't understand
>PCT.  I didn't say you won't be able to use PCT to make
>predictions. ================
>
>********************************************
>   Tom to Martin (in the present):
>Let me be sure I follow you correctly:  Not only do PCT modelers
>not understand PCT (your original claim); now modelers are akin to
>meter readers and have no need to understand PCT.

 I should know better than to tease people with serious agendas (can
one pluralize a plural knoun?).

But yes, when the meter has been designed and built, the meter reader
doesn't need to know how Maxwell's equations work.  When Bill has
designed the PCT structure, it doesn't take genius to fill in the
parameters without understanding the beauty and power of the theory.

I retract my original statement, which was mainly intended to provoke
Rick (he provokes me often enough that I felt entitled).  There are
many kinds of understanding, and one approach will suit one person while
being quite obscure to another person.  For me, Shannon theory explains
unambiguously why PCT works and why higher levels work more slowly on
average than lower levels, etc., etc.  It provides a rationale based on
fundamental facts of nature, rather than in the finding that PCT works, or
that we can see how evolution could have produced control hierarchies.

I like (Occam's razor) things that are consequences of other things we
know about nature better than things that stand off on their own, needing
new basic foundations.  It is in this sense that I say that one needs
Shannon if one is to understand PCT.  But there may be other ways of tying
PCT to fundamental natural laws.  If so, I would say that one could not
understand PCT without understanding those ties, either.

======================
>   Tom to Martin (in the present):
>Neither the model of the control system or the environmental
>phenomena with which it interacts need be linear.  Bill has
>published and posted on introducing nonlinearity into the PCT model
>and into the environment.  So has Rick.  I haven't, but I have
>tested the effects of nonlinearities in the coordinated systems:
>The models continued to function at the same level of realism.

Mea Culpa.  As I replied today to Bill, my problem was more of sloppy
wording than of poor understanding about nonlinearity.  You challenged
me with a linear problem, so I was thinking in those terms.  As you
can tell from reading that and other postings, I know very well that
nonlinearity is essential in the input (at least of a multilevel
control system) and not very relevant in the output.

>In the meanwhile, I wonder why so many people continue to assert
>that PCT models are necessarily linear and cannot explain and
>predict events when there are nonlinearities in the system or the
>environment.  Where do these ideas come from?  Why won't they go
>away?

I can guess.  It is because every formal didactic presentation uses linear
equations to describe the behaviour of an ECS.  The methods used to
solve the equations and demonstrate control would not work in a non-linear
system.  It is a natural step, for someone who is introduced to PCT through
the equations, to believe that PCT works only in linear systems.  The
ideas you get first are the hardest to dispel, but demos and the like
can help get rid of this one.

I'll think about your challenge.

Martin