# Model concepts

Hi Bill:
I would like to say ask a few things about the elementary
control module (ECM).

With respect to the basic closed loop diagram:

···

-----------------
<-----------------|Environment |<----
> ----------------- |
> D(-) ----------------- |
R----(+)->X--Ea------------->| G=??? |--------->O
^ (-) ---------------- |
> ---------------- |
------------------| H=1 |<-----
-----------------

** (D) disturbance, actually the weighted perceptual inputs, are
acting as negative feedback, therefore we should multiply this
by (-1) before adding it into the summer (or subtract it in the
appropriate way).

** The (X) is the summer/comparator junction.

** The (R) reference is the weighted perceptual inputs.

** Ea is the Error signal.

** What is G??? (I can only think that it is FNO + any other
internal functions working on the error signal {This was
deduced from matching the structure of the ECM to that of the
basic negative feedback model})

** Now, since I cannot see what (H) is, I assume it does not
exist as I have drawn it but, exists as the environment (as
drawn).

** Output (O) is what is sent out of the ECM, whether it be to
other ECMs or to the external environment.

This all started when I sat down and tried to model the steady-
state solution. Then I began to think about it and realized that I
didn't really know what (G) was. I mean, after that of course,
you have to abe able to recognize its form, convert it to the (s)
domain, solve for the partial fractions solution, or whatever
method, and finally use the inverse Laplace transforms to get
provide (Type 1 -step, Type 2 -ramp, etc.). I think these are
basic questions Bill, but I would like to have them clear in my
mind.

Another reason why I started this general analysis is because
I didn't know how to analyze "1+G", in order to determine the
optimum "S" in your dynamic slowing equation!!! So I'm in a bit
of a position...

I have your 1978 paper, "Quantatative analysis of purposive
systems: Some spadework at the foundations of scientific
pyschology", Pyschological Review, pg. 417-435, 1978.
I have started to review it.

Well, that's all. Thank-goodness.
Hope to hear back from you soon,
Chris.