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- Date: Mon, 7 Sep 1992 09:31:51 -0600
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- From: "William T. Powers" <POWERS_W%FLC@VAXF.COLORADO.EDU>
- Subject: Influence; e. coli model
- Lines: 90
-
- [From Bill Powers (920907.0900)]
-
- Greg Williams (920907) --
-
- Let's stay with the basic ideas for a while and make sure we
- understand each other.
-
- >Your "control by disturbance" is my "manipulation." Manipulation
- works >as you say, requiring "cooperation" of the manipulee. I must
- say, >however, that "control by disturbance" is important in another
- way to >BOTH the controllee AND the controller, since they ARE both
- controlling >in ways contributory to the outcome. And, in this sense,
- I think what >we control for IS important to us.
-
- I'm controlling variable v by means of action a. You apply a
- disturbance d to v. This causes v to depart from v*, my reference
- level for it, by approximatly d/myloopgain; my action causes a to vary
- enough to produce this result, so that a is nearly -d. So by varying
- d, you can cause a to vary. This is your control of my action. You can
- have a reference level a* for a. My action a will come to a state of
- about a*/yourloopgain.
-
- By this way, this takes no cooperation from me -- I don't have to pay
- any attention to my own action. All I have to do is continue doing
- what I was doing before: keeping v near to v*. From my point of view,
- your variations of d are just another disturbance. It doesn't matter
- to me whether those variations are systematically aimed at a goal of
- yours or are random.
-
- By our postulates (which forbid conflict), I must not have any goal
- that forbids my action a to be controlled by you. So my action can't
- be "important" to me -- that is, I can't have any goal for it, but
- must be willing to let it vary as you choose. I can't have any
- preference for a particular state of my action if you are to be able
- to control it without conflict with me. This procedure works best if I
- (higher level) pay no conscious attention to my actions at all, but
- just let the (lower-level) control system operate them.
-
- It has just occurred to me that we are probably using the term
- "important" in different ways. I suspect that you're using it to mean
- _objectively_ important -- that is, important in ways unknown to me
- but known to the manipulator (in the manipulator's opinion). The
- manipulator may believe that if he can get me to bring my action into
- the state a*, something good for me will result, or something bad for
- me will be avoided. The manipulator may, for example, have the opinion
- that if I could be maneuvered into learning the moves that result in
- taking square roots correctly, this action by me will be of future
- benefit to me even though I'm indifferent to it now and am not doing
- it "on purpose.".
-
- Is this what you're talking about when you speak of importance?
- ----------------------------------------------------------------------
- Hans Blom (920907) --
-
- I puzzled mightily over your e. coli Pascal model until I went back
- and read your description: "In my model, coli has neither a counter
- (memory) nor a sensor to sense gradients. I assume it is too
- primitive for either."
-
- What I was puzzled about was the lack of sensing of the gradient --
- there can be no control system without sensing. I was saying to
- myself, "Why, this is just a random-walk generator -- how could it
- ever go up or down a gradient?" The answer is, of course, that it
- can't, except by accident. This is why it always escapes off the
- screen eventually.
-
- To make this model behave like e. coli it's necessary to make the step
- size, or the delay between tumbles, depend somehow on the sensed rate
- of change of concentration. Your model is much too simple; the real e.
- coli (the intestinal bacterium) does have such rate-of-change chemical
- sensors, and does vary the interval between tumbles according to the
- time rate of change of concentration.
-
- What you have shown is useful, in that it shows that a bacterium that
- is too simple -- that is not a control system -- can't do what e. coli
- actually does.
-
- Rick, why don't you post the code for our e. coli model? I'm sure that
- Hans can translate the Apple-specific parts into his version of
- Pascal.
-
- By the way, Hans, could you set your right margin to about 70 or 72?
- Your lines are exceeding the screen width here, and I end up with lots
- of single words on a new line. I suspect this is true for most others
- too.
- --------------------------------------------------------------------
- Best,
-
-
- Bill P.
-