[Martin Taylor 971226 17:30]
Tim Carey (972612.0720)
Your posting puzzles me a bit. I tried to answer [Martin Taylor 971224 2215]
some questions in your message of (972412.0800) (the date is a bit puzzling,
too:-), that indicated you did not have the technical background to
understand how control works, for example:
What do you mean by a network?
Are we speaking about control systems within one person or between people?
What's a "coupling"?
How do you get a positive feedback loop? Can a negative feedback
loop turn into a positive feedback loop?
What's an amplifier?
What's a flip-flop?
What's an oscillator?
And several more of the same general nature. In addition, you made a lot
of comments that your _could not_ have made if you had a reasonably
substantial understanding of how control works.
I attempted to answer these questions and comments as best I could,
thinking it might help you to develop an understanding of control and the
kinds of thing that can happen when control systems interact. You reply
I don't know what impression you got from my last
post but I'm sorry if I've not communicated my position clearly enough. I
believe I _am_ learning about control.
If that is so, what was your reason for asking the questions and making the
commentsthat led me to believe you lacked the necessary background?
Was it purely an altruistic gesture, to get me to take the time to write a
tutorial for those who are less well informed? I don't mind doing that, but
I wrote it with the apparently false idea I would be helping _you_.
I have copies of demo 1 and demo 2 on
my computer which I go over from time to time, I have visited Bill's web
page, and I regularly do the demos on Rick's web page.
Well, that's good. But then why ask "what's an amplifier" and " how do
you get a positive feedback loop," and why make all those other comments
that suggested to me that you would benefit from studying the demos?
My point was that I
am _only_ interested in learning about control and I am having trouble
deciding what _is_ and _isn't_ "control-talk" in your posts.
_Everything_ in my messages has to do either with elementary control
systems or the interactions among elementary control systems. For many
of the phenomena that occur when control systems interact, it simply
doesn't matter that the interacting entities are control systems.
Interacting control systems have some special properties that interacting
non-linear amplifiers don't have, but in the context of a discussion of
David Goldstein's obsessive-compulsive issue, those special properties
don't come into play much. They _do_ come into play, as I tried to show,
when we get to issues such as why Leo Kay said he could control if something
important was to be done, or why his problem showed up more at home than
A network is a number of entities that have some kind of connection
between them. If you prefer mathematical terminalogy instead, it's
a "graph." One kind of graph or network is a road map, in which the
entities are cities and the connections are the roads.
Here's a good example Martin. I'm not interested in road maps, and I'm only
interested in "a number of entities" if these entities are control systems.
If you learn the basics, you can apply them where you want. If you don't,
all you will get is epicycles. I tried to use an analogy with which I
assume you are familiar, to answer a _direct_ question you asked. You
don't want the answer, fine. Don't ask the question. Networks of control
systems is what we are interested in. If you don't know what a network
is, how on earth can you begin to understand how networks of control
I find this a hard question to answer, without the necessary foundation.
But I'll try. Quick answer: the dynamics is the way something changes
over time when left to itself. Less quick answer: Think of a child's
swing, hanging from a tree branch.
Martin, I'm not interested in child's swings either.
I get the impression that you want only a description of the way the
movements of the planets look from central Brisbane, and wouldn't be
interested in how they might look from Adelaide, let alone that from
another viewpoint their motions might look like ellipses ("what's an
ellipse?") or that they might be succinctly described by three simple
laws and some measurements of their mass ("what's a mass?").
You wanted to know what I meant by dynamics...or did you? You said you did.
Why was that, if you did not?
Networks of control systems follow very complex dynamics, under some
fairly general coupling conditions, and the tighter the coupling, the more
likely it is that the control systems will not control well, if at all.
Change these couplings, and you can change the network dynamics--apparently
often to the benefit of the person concerned. There. I've used in one
sentence three terms you asked about, three critical terms. In my
answer to you, I used them in a context with which I assumed you might
be familiar. Having understood the terms in that context, I hoped you
would understand them in the context you are interested in. But no:
"I'm not interested in child's swings." Oh, well. Sorry to waste your
I think we have well and truly established that I am unable, at this stage,
to participate intelligently in a conversation that is "more general" I
think it would be ultimately more rewarding for both of us if we just stuck
to discussions about control systems.
Yes, it would be more rewarding if we just stuck to a discussion of the
retrograde motion of Mars than if we talked about the more general case
that massive objects attract each other. Yes, indeed:-(
systems. The organisation of _a_ control system is simple: one perceptual
input function, one comparator with a reference input, one output to the
environment. If the system is actually to _control_, that output must be
hitched to the environment in some way that allows it to affect the
perceptual input function in such a way that the error is reduced
Isn't the "hitching" of the output through the environment accounted for by
the feedback function?
I mean the couplings between the output function and the physical variables
that are arguments to the CEV function. That's part of the feedback
The "hitching" couplings and the perceptual input function together
account for the feedback function, _not_ the other way around. To say
that the feedback function accounts for the couplings between the output
function and the physical world is rather like saying that the retrograde
motion of Mars accounts for gravity.
disturbance signal source. Best to use "disturbance signal value," if
I understand your question properly, and the answer is "NO, the reference
signal is irrelevant to the disturbance signal value."
No, Martin I wasn't talking about how the reference is related to the
disturbance. I believe in your statement you were talking about the
disturbance causing actions. I was suggesting that the actions are caused
_not only_ by the disturbance but also by the reference perception that is
specified at that particular time.
Of course...and as I also said. If you missed my discussion of "cause"
a few days ago, I'll send it to you privately. If you want to pursue the
"cause" of the actions, don't forget the nature of the perceptual function,
the nature of the output function, and the organization of all the
supporting control systems in the hierarchy. And lots of other surrounding
I don't know how beneficial any of this discussion is for either of us at
This particular message probably isn't, since it is based on my total
confusion as to what you want to achieve, and the fact that you say you
understand how control systems function, but ask questions that suggest
just the opposite. I really don't know how to answer helpfully.
I really appreciate you taking the time to explain your
position and various ideas that are important to you, I just think we are
in very different places at the moment.
I'm not clear even what you mean by my "position." I have mentioned certain
facts, and speculated (and labelled as speculation) that those facts might
be relevant to a condition in real people. You enquired as to what I meant
by some concepts that are fundamentally necessary if you are to understand
the facts, and I tried to explain them. What "different places" do you mean?
I'm trying to deal with issues you raise, and provide some of the background
you appear to need in order to understand what I am saying--as you requested.
Maybe you could be clearer, and then I could perhaps be more helpful.