[From Rick Marken (2013.12.25.1315)]
···
Fred Nickols (2013.12.24.0828 EST)
FN: I wouldnt worry too much about it, Boris. Rick is probably as close to being the crown prince of PCT as anyone but hes far from infallible.
RM: I’ll think about this when I’m at the movies today and try to figure out if I should feel complimented or offended;-) But I want it to be clear that I will only accept the Crown Prince title if it comes along with a very large stipend;-)
FN: The CSG archives are full of instances wherein Bill corrected Ricks thinking.
RM: Yes, and it happened many times outside of CSG conversations as well. But I can remember at least once when I corrected Bill (I can’t remember what it was about now but I do remember that I was when we were visiting my sister iin laws at Xmas at her house nested in the gorgeous redwoods of the Santa Cruz Mtns. It must have been back in the mid 1990s.
FN: Sadly, without Bill, theres no one to do that anymore.
RM: While it’s true that no one can replace Bill, I think everyone as a right to “do that” – ie. correct me or anyone else – when they think there is an error. I think some things will just be bones of contention no matter what because there is really no way to solve them to any one’s satisfaction. But factual errors – errors that can be “objectively” tested – can be corrected. These are the kinds of errors that I remember Bill “correcting” for me – and that I accepted. And there were errors I made that I corrected on my own by demonstrating things to myself using modeling and testing. For example, I remember getting in a big fight with Bruce Abbott (as usual) saying that people really could not be controlled because (by disturbing a controlled variable) because their reference for the state of the controlled variable could change autonomously. I said that based on intuition but when I tested it it turns out that I was dead wrong; you can control another person’s behavior by disturbing a variable they are controlling even if their reference for the state of that variable is changing randomly. I confessed my error to Bruce and put the demonstration up at my wed site( http://www.mindreadings.com/ControlDemo/Coercion.html).
FN: So, Rick will doubtless put forth PCT as he sees it.
RM: What else could I put forth? What else could anyone put forth. My only hope is that I (or others) catch me when I get of track; that I am always open to correction (hard to do but I try) and hope that others are as willing to be corrected.
RM: But if he errs he wont go unchallenged, just uncorrected.
FN: I hope you are wrong about that. I hope there are people who will not only challenge me but who are capable to providing useful correction. All we’ve got is each other, after all.
FN: And thats okay; his grasp of PCT is probably as good as any others out there, just slightly different in some ways, as attested to by the occasional disputes and discussions between he and other equally savvy PCTers.
RM: Hopefully these differences, to the extent that they are differences that make a difference (and I think many are) can be ironed out through modeling and test. That’s my “faith” anyway. Bill was exceptionally brilliant but I know that he never wanted PCT to be about him. He didn’t want to be the guru, which meant he didn’t want his pronouncements to be taken as gospel. Bill was staring a new science – just as Newton was starting a new scsience – and he should be celebrated for that. But now we have to carry on the science, build it up and do it. And we have to do it without Bill to “correct” us (and he was not always correct, just as Newton was not always correct). Science is a human endeavor and human endeavors often involve conflict; but in science I would hope that these conflicts can ultimately be resolved, not by going to sacred texts and saying but via modeling and experimental test.
FN: So relax and have a happy holiday season. The new year should keep us all busy.
RM: Yes,let’s have a nice, scientific New Year. And many more after that.
Best regards
Crown Prince Rick
Fred Nickols
From: Boris Hartman [mailto:boris.hartman@MASICOM.NET]
Sent: Wednesday, December 25, 2013 7:42 AM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: Re: Classical Control Systems Lectures
Well Rick, I must admitt I am worried where this “PCT boat” is goimg
[From Rick Marken (2013.12.22.1110)]
On Sun, Dec 22, 2013 at 2:53 AM, Boris Hartman boris.hartman@masicom.net wrote:
HB:
TO PUT IT EXACTLY IN PCT SENSE, CONTROL IS : “Achievement and maintanance of a preselected perceptual state in the controlling system, through actions on the environment that also cancel the effects of disturbances” (B:CP, 2005).
RM:
Yes, that’s a good one too;-) It’s tough to give a definition of control that is completely theory free and I don’t think Bill was trying to do that when he came up with this definition. Indeed, part of Bill’s goal in giving this definition of control was to include the important new assumptions of what has come to be called PCT. I don’t think it was until many years after the publication of B:CP that he actively promoted the idea that control was a phenomenon in and of itsef – an objective fact (as in the subtitle to LCS III) – that is explained by the theory of control: control theory.
HB :
I’m wondering if you become an “officiall interpreter” of Bill’s knowledge ? J. I thought you are just moderating. And from one subtitle you concluded that “control” is “objective” fact.
The “fact” in subtitle could also mean that there are so many evidence and models that we can conclude the generality of control in living beings. If you think that Bill showed for “objectivity” in external environment, you’ll with no doubt find some evidence in the book LCS III and show me that you are right.
It seems to me, that you are trying to reduce PCT to some special case of PCT. But in this way PCT will fall apart like “castle from cards”. Beleive me. Bill was smart guy, knowing what he was doing, and why he wrote definitions as they are. He kept generality of PCT model. And you are not. Control units can be used in many ways, not just for “protecting” the “controlled” variable from disturbances. Think of it.
Control “being a fact” is by my oppinion also contradiciting your previous statement that “control” is phenomenon, so it’s by my research in vocabulary, entirely dependent from perception. And perception can never be “objective”. Maybe you had in mind some other meaning of “phenomenon”.
There is no “objective fact” on itself, because you have to prove that you somehow directly access to “reality” (outer environment) and know it in every detail. But still humans are knowing about “reality” only through their perception (some transformations) of “reality”. And perception is not only limited, but it’s also just partly presenting the “reality” or outside environment (as much input functions you have) and input gain. Mostly enough for good control, but sometimes is not enough. Accidents happens.
And more perceptions of the same “reality” more “objective fact”. “Reality” is never mirrored into your consciousnes to be “objective”. Whatever you are perceiving is just a “model”, “perceptual construction”, “abstract system”, whatever you call that what you perceive.
RM :
I think the definition above can be “objectified:” a bit by changing “perceptual state in a controlling system” to “variable”. The idea that it is a perceptual variable that is controlled is really part of the theory – a very important part of the theory but part of the theory nevertheless.
HB :
“Objectifying” Bill’s definition with “variable” is not good idea. As I said before. I’m pretty sure that Bill knew what he was doing. But I’m not sure that you do. I think that’s why his definitions and generic diagram survived so much time, and I beleive it will survive much more time in future, if you will not change or modify it. Putting the controlled “variable” into Bill’s definition and consequently into “functional” diagram could by my oppinion destroy it’s generality. It could be meant as just one special case of PCT.
RM :
But one can observe control without making any assumptions about how control works. We can do this by observing a variable, such as the distance between cursor and target in a tracking task, and noting that disturbances have little or none of their expected effect on this variable and that this is because the effects of these disturbances are being cancelled by observed actions (mouse movements).
HB :
I thought that you are “protecting” the “controlled” variable form distrubances not canceling the effects of disturbances.
Why did you use term cancel instead of term “protecting”, if they have the same meaning by your oppinion ? And sorry I didn’t get it, which is “controlled” variable in this case that you are “protecting” it from disturbances ?
RM :
So control is happening because we are seeing the:
“Achievement and maintenance of a variable in a particular state through actions on the environment that also cancel the effects of disturbances”.
HB :
So you are also “officialy” promoted to change Bill’s definitions. To me it’s obviously that you shouldn’t do that. Now as you changed definition, you’ll have to change also his generic diagram and put the “controlled variable” into outer environment. Well I’m wondering, are you going to change whole his theory? Into what, RCT ?
RM :
I also got rid of the term “pre-selected” because this also makes theoretical assumptions about what is going on inside the system doing the controlling.
HB :
You got rid of Bill’s term in his definition (???). I’m really wondering who authorised you to do that ?
RM :
Of course the “variable” referred to in the above definition is a perception but then everything is a perception so it’s really unnecessary to mention it.
HB :
Better. Nothing is “objective”. All is just perception. Variables are just perceptual characteristics. But in your case I see it necesary to mention it, as you are mixing “objective facts” with perceived states of variables.
And I’m asking you once again that you use sysmbols HB not BH. As I will thought that you are reffering to Bob Hintz.
BH: So as I see it, control is initially not “protecting” act but cancelling act of output which compensate effects of disturbances so to maintain perceptual stability (some preselected perceptual state) in the controlling system.
RM: That’s fine. The verbal description matters less to me than the functional model that actually makes control work.
HB :
Well, I’m glad that you are satisfied with my verbal descriptions. But I still think that verbal description are mostly closely related to “functional models” in our heads. And I’m pretty interested if you can show me your "functional« model (not adapted Bill’s), that will show how control unit is “protecting” controlled variable in outer environment. I’d just like to see how much your verbal description is not important to you and how “actualy makes control work”.
RM :
I think that control can be correctly described as involving “cancelling” the effect of disturbances or “protecting” a controlled variable from the effects of disturbance. But if “protecting” doesn’t work for you then feel free not to use it.
HB:
This one is very »foggy« and »slippy« conclusion. I think that you shouldn’t use this “equatation”, specially not in Bill’s defintions. But I think you could use it in some of your theories.
But to test rightness of your “equality”, I’d be glad if you show us how examples about PCT that Bill used with his favourite terms work. So please show us how you would verbalize his examples with term “protection”. Maybe something like this :
- driving control (“protection” of speed and position on the road),
- tracking experiment (“protection” of position of cursor) .
- maybe you’ll remember some more.
As always maybe I misunderstood something sorry
Best
Boris
From: Control Systems Group Network (CSGnet) [mailto:CSGNET@LISTSERV.ILLINOIS.EDU] On Behalf Of Richard Marken
Sent: Sunday, December 22, 2013 8:12 PM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: Re: Classical Control Systems Lectures
[From Rick Marken (2013.12.22.1110)]
On Sun, Dec 22, 2013 at 2:53 AM, Boris Hartman boris.hartman@masicom.net wrote:
BH: TO PUT IT EXACTLY IN PCT SENSE, CONTROL IS : “Achievement and maintanance of a preselected perceptual state in the controlling system, through actions on the environment that also cancel the effects of disturbances” (B:CP, 2005).
RM: Yes, that’s a good one too;-) It’s tough to give a definition of control that is completely theory free and I don’t think Bill was trying to do that when he came up with this definition. Indeed, part of Bill’s goal in giving this definition of control was to include the important new assumptions of what has come to be called PCT. I don’t think it was until many years after the publication of B:CP that he actively promoted the idea that control was a phenomenon in and of itsef – an objective fact (as in the subtitle to LCS III) – that is explained by the theory of control: control theory.
I think the definition above can be “objectified:” a bit by changing “perceptual state in a controlling system” to “variable”. The idea that it is a perceptual variable that is controlled is really part of the theory – a very important part of the theory but part of the theory nevertheless.
But one can observe control without making any assumptions about how control works. We can do this by observing a variable, such as the distance between cursor and target in a tracking task, and noting that disturbances have little or none of their expected effect on this variable and that this is because the effects of these disturbances are being cancelled by observed actions (mouse movements). So control is happening because we are seeing the:
“Achievement and maintenance of a variable in a particular state through actions on the environment that also cancel the effects of disturbances”.
I also got rid of the term “pre-selected” because this also makes theoretical assumptions about what is going on inside the system doing the controlling. Of course the “variable” referred to in the above definition is a perception but then everything is a perception so it’s really unnecessary to mention it.
BH: So as I see it, control is initially not “protecting” act but cancelling act of output which compensate effects of disturbances so to maintain perceptual stability (some preselected perceptual state) in the controlling system.
RM: That’s fine. The verbal description matters less to me than the functional model that actually makes control work. I think that control can be correctly described as involving “cancelling” the effect of disturbances or “protecting” a controlled variable from the effects of disturbance. But if “protecting” doesn’t work for you then feel free not to use it.
Best
Rick
This could mean that “controlled variable” is already affected and new state perceived and controlled in comparator and act of canceling the effect or compensating the efect of disturbances realized.
To use term “protect” is something that means for me to act in advance, so to “prevent” some “controlled variable” or better predefined state of controlling system, from being disturbed, displaced, affected etc.
Term “protecting” is probably kind of control but not in initial sense. By my oppinion is one of consequences of “pure” PCT control, which is by definition used with terms canceling, compensating, etc
Something similar was Ashby’s “control” definition : “Every stable system has the property that if displaced from a state of equilibrium and released, the subsequent movement is so matched to the initial displacement that the system is brought back to the state of equilibrium” (Ashby, 1960).
I think that Ashby used “compensation” for description of “control”. And it seems to me that he used terms to describe actual “displacement” and actual “compensation” not something happening in advance.
He tried to give also definitions of dynamic system, variable and system, specifications of behaviour, “stability”, “equilibrium”, “steady-state”, and so on, as I think that Bill used some of this terms in Appendix to the book B:CP, 2005.
So the main point I see, is that whatever “controlled variable” is meant, is first “moved” (perceived displacement) from the predefined, initial state (reference state, equilibirum ) and than by canceling or compensating or opposing effects of action or whatever we call that (maybe behavior), again brought back to predefined, initial state (reference, equilibrium, whatever ).
If we say that “controlled variable” is protected than you probably assume that “controlled variable” was not disturbed yet, as disturbances has already been cancelled, compensated by control system in advance. But that can never happen if control system “has no experiences” with “moving controlled variable” from initial state with certain disturbances. How else could control system “choose” disturbances to act on, so to protect “controlled variable” from being affected if control system doesn’t know what kind of effect distrubances have on “controlled variable” and system itself.
I think that the selection of disturbances that could have effect on controlled variable, are those which in the past show tendency to “displace controlled variable” from initial state. So when control system has that “experience” than it can probably reorganize so to “protect” it from disturbances. But by my oppinion it has to be complex control system, build up with many control units, what could happen through evolution.
In such a complex organized control systems (more organized control units), certain control units serve the goal to really “prevent” or “protect” certain “controlled variable” from being disturbed, displaced or “moved” from initial state like in some physiological cases.
So I think it’s better to use initial terms when making defintion about control in PCT sense such as cancelling, compensating activity not “protecting” activity.
Your “exclusive” statement about Gordon . :
RM : “Well, Mr. Douglas is now off my list of people to listen to about control theory. This lecture was awful”.
has no sense to me.
By my oppinion Douglas tried methodically to show how control in different dynamic system works. And by my opinion his retorics and pictures about control is better then yours about “protecting controlled variables”. But both are insufficient (as probably mine is), but that doesn’t mean that we have to stop talking about your and his presentation of control, because they are “awfull”. I think that both are good as the bases to improve them, so they would show better how control theory works.
Rick, you are doing a good job, moderating on CSGnet. But nobody said that you couldn’t be better J
I can’t comment other discussions for the time being as I didn’t read them. Maybe I missed something important. I also didn’t entirely follow the discussion about B:CP (2005) so I’m interested if you make any comments about Appendix in the book. There are some interesting clarifications of terms control, stability
Best,
Boris
From: Control Systems Group Network (CSGnet) [mailto:CSGNET@LISTSERV.ILLINOIS.EDU] On Behalf Of Richard Marken
Sent: Saturday, December 21, 2013 2:38 AM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: Re: Classical Control Systems Lectures
[From Rick Marken (2013.12.20.1740)]
Martin Taylor (2013.12.20.11.47)–
RM: Stability and control are two different phenomena, something that it is now clear to me that Mr. Douglas is completely unaware of. These two different phenomena are produced by two different kinds of systems; stability is a kind of behavior exhibited by certain “open-loop” or what I call “causal” systems.
I still haven’t looked at the videos, but it strikes me that you are doing the old philosophers’ trick of taking a word that has a variety of meanings, and using a meaning appropriate in one context as though that were the meaning appropriate to a different context. Yes, “stability” and “control” are indeed different phenomena, in the same way “food” and “vegetable” are different concepts.
RM: No,“stability” and “control”, as described by Douglas in the very first control lecture, are different phenomena in the way “food” and “poison” are different. A stable system (according to the lecture) is one that returns to its original (“equilibrium”) state after a transient disturbance; a control system is is one that remains in a reference state during continuous disturbance. Douglas should have talked about variables rather than systems but you get the idea.
MT: All feedback loops, in fact all dynamical systems, whether control systems or not, have stability criteria. Either they are stable or not. Some are more stable than others.
RM: Yes, they do. Indeed, I measure control in terms of stability (observed/expected variance of the variable). In this case “stability” is simply referring to a measure of the observed variations in a variable and it can be used to measure the variability of a controlled variable or an uncontrolled variable (like the variable position of the ball in the bowl that Douglas refers to as a stable system).
MT: Some are metastable, meaning they will maintain their current values until something momentarily disturbs one of their signal values. Some of those will continue to diverge from the original metastable value after the disturbance, some will just maintain the disturbed set of signal values without further change. Some are absolutely stable, meaning that after any kind of momentary disturbance they will return their values to their original levels. Most real systems don’t do that, and are stable only if the momentary disturbance doesn’t exceed some limit.
The key concept is the “orbit”. All systems that can be described by a vector of variables have a state. Their state is the vector of current variable values together with the rates of change of the current variables. That includes control systems, ball-in-a-bowl systems, the synapse strengths of networks of millions of neurons, etc. etc. If the system is at some location in the state space and is not further disturbed from outside, it will follow some track through the state space. That track is an orbit, and there is only one orbit through any point in the state space.
A stable system is one for which the orbit will converge to some track that is the same for all the initial locations in the state space. That track is called an “attractor”. The attractor may be a fixed point, a closed path (which represents a stable oscillator) or a “strange attractor” (which I won’t explain now). An unstable system is one for which the orbits diverge. Here are a couple of examples of attractors, or at least the projections of them into two dimensions, because even in 2-D, the orbit is actually in a space of four dimensions, two for location and two for velocity. I have omitted the velocity coordinates in these examples, and in the fixed-point example it is the velocity that distinguishes the orbits where two of them cross in the figure. In the 4-D state space, only one orbit passes through any particular point.
RM: All of this simply describes the observed behavior of a variable. Nothing about the shape of these orbits can tell you whether the variable is controlled or not.
MT: A control system is one for which the attractor converges in at least one dimension (the perception-value dimension), but that’s not the main criterion for differentiating the “ball-in-the-bowl” from a trivial control loop.
RM: That’s not only is not a “main” criterion; it’s not a criterion at all. The only criterion for distinguishing the “ball-in-the-bowl” from a controlled ball in the bowl is the criterion John Kirkland just mentioned: The criterion of The Test for the Controlled Variable, which is whether there is less of an effect of a disturbance on the controlled variable than expected. You simply cannot tell, by looking at just the observed behavior of the “ball-in-the-bowl” (like the “fixed point” and “stable oscillator” orbits pictured above) whether you are observing the behavior of a controlled or uncontrolled variable. The orbits plotted above could be the behavior of a controlled or uncontrolled ball. This is exactly analogous to the situation in my mindreading demo (http://www.mindreadings.com/ControlDemo/Mindread.html). When you move one avatar around the screen in a controlled manner, the other two move as well; you can’t tell from the movements (orbits) of the avatars, which is controlled and which are not. In order to determine control you have to disturb the position of the avatars and see which avatar is affected least by the disturbance.
MT: Bruce Abbott put his finger on it when he pointed out that the ball-in-the-bowl uses the energy supplied by the disturbance to return the ball to its fixed point, whereas the control loop uses an independent energy supply to oppose the effect of the disturbance on one (and only one) of the variables in the state space of the loop. The manner in which control is established is irrelevant.
RM: This is a description of models that produce the observed behaviors: the open loop physics model for the “ball-in-the-bowl”; closed-loop control for the controlled ball. The manner in which control is established may be irrelevant (I have no idea what that means actually; the only way I know of to establish that control is happening is by using the Test) but one has to have established that control is going on in one case and that it’s not going on in the other in order to apply the correct explanations (models) to each case.
MT: It so happens that the PCT definition of control is the maintenance of one particular value among the many different signal values in a negative feedback loop, so Rick’s comment “Control is produced only by negative feedback control systems” is a tautology.
RM: Actually, that’s not the PCT definition of control. The definition of control is “maintenance of a variable in a pre-selected state, protected from disturbance”. A negative feedback loop is a model of how control works. It’s not a tautology.
MT: Control is produced only by negative feedback control systems. So I couldn’t disagree with you more when you say “we need to be sure that stability and control are not seen as belonging to different kinds of systems”. In fact, we need to be VERY sure that we understand that stability and control “belong” to two very different systems: open-loop, causal systems for the former and closed loop negative feedback systems for the latter. [MT: “you” here is Bruce Abbott.]
RM: So let me get this straight. Are you saying that the “stability” of the behavior of the “ball-in-the-bowl” is the same as the “stability” of the behavior of, say, the water level in Ktesibios’ water clock?
Best
Rick
To which I can only say that there are several applicable proverbs along the lines that one is better advised to listen and learn rather than to guess and pontificate. Bruce is quite right to say “we need to be sure that stability and control are not seen as belonging to different kinds of systems”. To contradict Bruce is to say something as nonsensical as “we need to be sure that leafiness and trees are not seen as belonging to different kinds of objects”. “Stability” applies to all kinds of dynamical systems, which control systems are.
Martin
–
Richard S. Marken PhD
The only thing that will redeem mankind is cooperation.
– Bertrand Russell
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Richard S. Marken PhD
www.mindreadings.com
The only thing that will redeem mankind is cooperation.
– Bertrand Russell
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–
Richard S. Marken PhD
www.mindreadings.com
The only thing that will redeem mankind is cooperation.
– Bertrand Russell