[From Bruce Abbott (951205.1745 EST)]
Bill Powers (951205.1245 MST) --
Bruce Abbott (951205.1320 EST)
I am maintaining that if the reinforcer did not tend to reduce
error, it would not serve as a reinforcer. Within the control
system, a constant disturbance would tend to increase the error;
the system will reach an equilibrium in which the reduction in
error supplied by the reinforcer will just balance the increase in
error supplied by the disturbance, so one will not _observe_ any
further reduction in error once this state is reached;
nevertheless, the reinforcer continues to supply an error-reducing
effect on the controlled variable each time it occurs as a result
of control-system action. If it ceased to provide this service, it
would cease to function as a reinforcer.Your premise that "a constant disturbance would tend to increase the
error" is false. A disturbance may act either to increase or decrease
the error; in either case it is a disturbance, and in either case it is
resisted by an opposing change in the action of the control system.
If you read just a little further (past the semicolon that denotes the start
of the subordinate sentence that served to explain my assertion), you will
see that I am referring to the steady state, after the system has come to
equilibrium and the system is generating a constant output that just offsets
the tendency of the constant disturbance to increase the error. Under this
condition the constant disturbance is having only one effect and one effect
only on the error: it is pushing in a direction that would increase the
error if the control system did nothing to resist it. This is what I meant
when I said that "a constant disturbance would tend to increase the error."
I am specifically NOT talking about comparing the error BEFORE the constant
disturbance was applied, to the error AFTER (i.e., the case to which your
explanation applies); I am talking about what is going on in the steady
state after equilibrium with the constant disturbance has been attained by
the loop.
Now that we have this cleared away, how does the rest of what I had to say
in that post sound to you? Make sense?
Regards,
Bruce