definitions of control

[From Bill Powers (960701.1130 MDT)]

Hans Blom (960701) --
[Writing to Rick]

     Control engineering was my major in University and it made up a
     great deal of my professional activities after that. So don't tell
     me I don't know the meaning of the word control. Has it ever
     occurred to you that maybe YOU make the meaning so idiosyncratic
     that discussions become almost impossible?

This is ONLY a matter of custom. What we are concerned with in PCT is a
system that can maintain its inputs at whatever momentary reference
value exists for the system. In the general case, which is the only one
worth pursuing in a general model, there will always be variations in
the reference signal at the same time that independent disturbing
variables are acting to alter the controlled input.

It's possible to consider special cases -- disturbance-free environment,
disturbances that occur only in one predictable pattern, constant
reference signals, square-wave variations, and so forth. But giving
different names to the system for each case hardly seems necessary, when
one basic model handles them all. It is possible that for special cases,
there are ways of optimizing the parameters of a system so it works best
for that case. But from all that I have seen, the differences in
parameters and in performance are minor and hardly worth making into an
issue. There is no difference in architecture between what you call a
"stabilizing" control system and a "regulating" control system. And in
human beings, EVERY control system must be usable for BOTH applications.

The only real issue here is whether we ought to use the word control
when talking about open-loop effects. In all such cases of which I know
where the word "control" is used, the loop is actually closed, but the
path by which it is closed is taken for granted and assumed to be
outside the range of the discussion. That is, one can make a case for
open-loop control only by ignoring the fact that someone or something,
somehow, must observe the output, compare it with a desired output, and
adjust the system so it continues to produce that output. True open-loop
control, in which the output is never observed or the observation is
never fed back to modify the system, is impossible. You couldn't even
set the system up to work properly.

Finally, Hans, don't forget that even though your major was control
engineering, you still learned what you know from other people, and they
learned what they know from still others. Wrong ideas are taught quite
as often as right ones, and errors can be propagated all too easily in
that way. There are, after all, departments of psychology in which all
sorts of ludicrous notions are passed solemnly on to succeeding
generations, all with the assurance that they have the stamp of
scientific respectability. It is possible that some of your mentors had
an ideosyncratic concept of what control means, and managed to persuade
you that it was universally accepted and objectively right. But that
doesn't mean they had a good definition of control -- only that they
insisted that you agree with it if you wanted to get a degree.

···

-----------------------------------------------------------------------
Best,

Bill P.

[Hans Blom, 960702b]

(Bill Powers (960701.1130 MDT))

                             It is possible that for special cases,
there are ways of optimizing the parameters of a system so it works
best for that case. But from all that I have seen, the differences
in parameters and in performance are minor and hardly worth making
into an issue.

The quality of control is hardly an issue? According to my under-
standing of evolution theory, it ought to have been a major issue in
shaping organisms into what they are today.

There is no difference in architecture between what you call a
"stabilizing" control system and a "regulating" control system.

There can but need not be a difference in architecture, although
your choice of only an integrator in the output function tunes the
system to stabilization and makes it pretty bad at tracking rapid
setpoint changes (including a simple proportional term would help a
lot). But there needs to be a difference in control parameters. If,
however, the output path contains only an integrator, this issue will
not come to light. That may be the reason why you have never dis-
covered it.

And in human beings, EVERY control system must be usable for BOTH
applications.

Yes. That might imply that a human control system might want to do
some real time parameter adjustment. Is that an issue that you have
investigated?

But please come back to the arguments I presented to Rick. Martin
said:

The short answer is that behaviour can change all over the lot
for any value of a reference condition.

And I said:
... the perception must track the effects of the actions in order for
feedback to be possible. So if action changes all over the place,
chances are that perception will do the same. ... If there is
circular causality (and a constant reference value, as is stressed
time and again), you can express any variable as a function of the
others. That is simple math. But the interpretation of the math is
clear as well: if behavior [action] can change all over the place,
HOW COME IT CHANGES IN EXACTLY THE RIGHT WAY?

Finally, Hans, don't forget that even though your major was control
engineering, you still learned what you know from other people, and
they learned what they know from still others. Wrong ideas are
taught quite as often as right ones, and errors can be propagated
all too easily in that way. There are, after all, departments of
psychology in which all sorts of ludicrous notions are passed
solemnly on to succeeding generations, all with the assurance that
they have the stamp of scientific respectability. It is possible
that some of your mentors had an ideosyncratic concept of what
control means, and managed to persuade you that it was universally
accepted and objectively right. But that doesn't mean they had a
good definition of control -- only that they insisted that you
agree with it if you wanted to get a degree.

When I read this passage, I was initially flabbergasted. Then I broke
out in a belly laugh louder than I've had in quite some time. You
have a great sense of humor. Thank you!

By the way, ever heard of projection?

Greetings,

Hans

Mr. Remi Cote 2204.050896 EST

I have a Quest...ion for the expertise of this net:

Suppose you have an empty glass on an outdoor (picnic) table.
Then the rain begin (heavy) and the glass is filled with the
pouring rain. When the glass is full to the brim, there is an
overflow, the glass is overflowing until the level of water
reach a level of reference, which is the level of the rim.

If disturbance (rain) continue the system somehow compute the
diference between the level of water and the level of the rim
and conteract on environement to reduce this discrepancy.

By doing this the Glass actually control his perception. Just like
E-coli do when he or she is controling perception of chemical.

So we have a psychology of glass...

I am having these strange thought because of a guy named Buckminster
Fuller. This guy wrote a book about the life of triangle...
He design the american pavillon in montreal (for the 1967 world fair)
I am sure most of the people of this net know him.

So is there any comment on what I propose. Is A glass of water a purposive,
control system?(in my example)
Thank
Remi