[From Bruce Abbott (960201.1820 EST)]
Bruce Abbott (960201.1020 EST) --
Has the spark gone out of your romance?
Not tonight, Bruce, I have a headache.
Not again! Damned disappointing . . .
How about a comment on your use of control, influence, and determine as
if they had equivalent meanings?
I had some thoughts about that while writing my retrofaction (now
spontefaction) tutorial. Control as used in EAB is one of those words that
admits of degrees -- on can talk of stimulus control as being strong, weak,
or even absent under given conditions. Because the stimulus is not viewed
as _causing_ a given response, but only as affecting its liklihood of
emission, it would not generally be proper to say that the SD _determines_
the response; it is only an influence. However, the term "control" could
also be used when the state of one variable _determines_ the state of
another. This is the sense in which it is sometimes used by engineers, who
might speak, for example, of a "motor controller" that "controls" the
rotational speed of a motor, even though what is being referred to is an
open-loop system in which the setting of the controller determines the
amount of current flowing through the motor's windings. I used the term
"control" in both senses when describing the spontefaction system.
I noted that the disturbance would control (determine) the spontefacted
variable in the absence of spontefaction. In the presence of spontefaction
the influence of (control by) the disturbance diminishes so that it is 1/(1
+ G) proportion of the unspontefacted amount, where G is the loop gain of
the system. In EAB terms I guess we would say that control over the
spontefacted variable would weaken as G increased. On the other hand,
control over action by e would be strong, since in the example system a is
completely determined by e once the output gain has been fixed.
But this got me to thinking about how "strong" and "weak" control would be
defined. One sense of it is that Variable A has strong control over
Variable B if Variable A represents the major source of variation in
Variable B. But another sense appeals to how much A has to vary (in
proportion to its normal range of variation) to produce a given amount of
variation in B (in proportion to its normal range). This second definition
is closer to the idea of "sensitivity." Both ideas seem to be tied up
together in the idea of "strength" of control, in the EAB sense of the word.
I wonder what a good metric for this would be.
By the way, the disturbance would appear to exert excellent control over
system output so long as the reference signal remained constant, while
exerting very weak (perhaps even undetected) control over the sfv.
Regards,
Bruce