[From Bruce Abbott (950507.1955 EST)]
Bill Powers (950507.1815 MDT) --
Bruce Abbott (950507.1855 EST) --
This type of control system is often referred to as an ANTICIPATOR
since the derivative control causes changes in the output forcing
function in anticipation of an error in the immediate future.
(Milhorn, 1966, emphasis mine)
Here is a more up-to-date quotation. Since everything that appears in
print is true, except that more recent printed comments are more true,
this statement must supercede Milhorn's.
The common practice of calling rate feedback "anticipation" is a
metaphorical usage and should not be given scientific credence.
Anticipation implies knowledge of the future, but rate feedback
depends only on knowledge of the past. (Powers, 1995, message
Well, if newer is truer, then I'm right and you're wrong! [I'm newer.] I
never thought debates on truth would be so easy to resolve... (;->
Seriously, I didn't intend that quote as support for the practice (i.e.,
it's right because most everybody believes it), but only as a [rather
amusing, I think] sidelight on our discussion, i.e., that the interpretation
Rick initially offered for his model's behavior is consistent with standard
However, now that you've resurrected your old statement, I would point out
that what "anticipation" is is a matter of definition. If anticipation is
defined to require knowledge of the future, then it does not exist (unless
you happen to be omniscient). Anticipation as we ordinary mortals define it
is based on experience. I anticipate that the sun will rise tomorrow, not
because I can see into the future, but because the sun has done so with
striking regularity in the past.
And this, being the most recent word on the subject, is true.