[Avery Andrews 930412. 1608]
(Rick Marken (930411.1700))
>The fact of the matter is that the input
>is not involved in directing the output AT ALL; input is DIRECTED by the
>reference signal (via the closed loop). That is, output is neither a function
>of input nor of input and reference levels together.
It depends on the time-scales -- if you're analysing things on a time
scale smaller than the transport lag around the loop, then output
is determined (`guided' was a bad choice of word, I think) by input and
reference level jointly. On a larger time scale, the input is
determined by the reference level, just like Rick says.
>If the Canadians are
>ever able to get past the cause-effect model into PCT they will have a
>FAR deeper understanding of PCT than those who listened to the PCT side
>of the debate, shrugged and said "everybody knows that". In fact,"hardly
>anybody knows that".
There is quite a lot that everybody does indeed know, and repeating it
over and over again does not assist people in noticing the stuff that
they actually don't know (like, behavioral scientists who think that
feedback is old hat don't seem to have noticed that they have no
methodology for ascertaining refererence levels, and therefore
have no chance at all figuring out what's going on if what they're
looking at is a hierarchy of control systems).
And I don't see the Canadians as being any more mired in the
cause-effect model than you are--as far as I can see, they agree with
me in seeing `cause' and `effect' as an expository vocabulary which
is sometimes useful in conveying a preliminary sense of what is going
on, but is in no way a substitute for understanding the principles
that are actually in operation (so that, on a short time scale,
input and reference level `cause' output, on a longer one, where the
loop gets closed a few times over, reference level `causes' input).
Avery Andrews@anu.edu.au