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UCD-STAFFORDBEER  October 2009

UCD-STAFFORDBEER October 2009

Subject:

Re: Control and the Law of requsite variety

From:

Roger Harnden <[log in to unmask]>

Reply-To:

Forum dedicated to the work of Stafford Beer <[log in to unmask]>

Date:

Thu, 8 Oct 2009 09:02:50 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (236 lines)

> John,
>
> This feels right to me,

Roger
On 7 Oct 2009, at 22:09, John Waters wrote:

> Nick
>
> Can you help me to get my understanding straight on this?
> As I see it
> (1) variety is an informational measure, equivalent to the
> Shannon-Wiener measure from a particular perspective, variety being
> specifically a measure of the number of possible states of a system at
> any particular time. Therefore
> (2) variety is generally difficult to measure absolutely but helpful  
> in
> making comparisons of information-carrying capacity. Therefore,
> (3) in practice, variety can help in defining bounds on
> information-carrying capacity (and therefore on the rate of change)
> within various parts of a system not easily measured or specified; so
> (4) a homoeostatic system can be defined crudely (but often  
> adequately)
> in terms of variety within a system resistant to precise and detailed
> modelling (in the "soft sciences") but
> (5) in practice a system open to more precise observation and
> measurement can be controlled more effectively (with minimal waste,
> damage, etc.) - hence the importance of the concepts observability and
> controllability in multivariable, optimal, well-defined control  
> systems.
>
> I may be missing your point, so please bear with me, but it seems to  
> me that
> (a) RV remains applicable in principle at any precision but becomes
> progressively less helpful in comparison to the direct measurement of
> system dynamics (to arbitrary orders of derivative) where a model  
> can be
> more precisely and clearly defined (in the "hard sciences"); but
> (b) RV can be employed usefully to control complex systems that elude
> precise or detailed modelling.
>
> John (:
>
>
>
> Nick Green wrote:
>> Money, man hours, digital computer programs etc are finite precision.
>> But air pressure is an infinite precision variable even tho we only
>> measure it to 4 decimal places or so. If you model air pressure
>> (fluctuations in density can be fun if dangerous) you can have nasty
>> surprises but if you know your man hours you know what you'll get
>> paid. So RV works for pay but great care is needed in climate  
>> modeling
>> etc. Imagine you have to take the difference of two natural variables
>> to find, say an equilibrium point e.g. the height of a flying
>> aircraft. It always wobbles up and down a bit- we call it noise (you
>> probably have a more precise tech term) but it is determined by the
>> difference of pressure under the wing and over the wing. Because so
>> many differences are involved great care is needed in finite  
>> precision
>> digital computing- (if forecasting the height wobbles accurately can
>> be done at all). Wind tunnels may be better at this. There the air
>> pressure is natural. You may have to go down to the molecular level  
>> to
>> convince yourself of this till one more molecule emitting a photon of
>> some energy going up under the wing causes the aircraft to rise a
>> small amount or one more over the wing produces a stall. This is the
>> cybernetic equivalent of infinitesimals in calculus but an important
>> constraint on modeling.
>> Pask would speak of incommensurability in this context and his No
>> Doppelgangers edict- no two things can be the same if infinite
>> precision is needed to compare them. All this needs a lot more work
>> but Pask opened this door and I report it as best I can- and hey its
>> your actual Advanced Pure Cybernetics! - confronted with these
>> uncertanties the aero engineer just adds redundancy- makes the wing a
>> bit stronger than it need be, as it were. You, I imagine, move the
>> controls as little as possible to stay in the narrow stable envelope.
>> What a shock it was (to me) to discover the constraints on high
>> altitude stall!
>> ----- Original Message ----- From: "Arthur Dijkstra"
>> <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Wednesday, October 07, 2009 5:03 PM
>> Subject: Re: Control and the Law of requsite variety
>>
>>
>>> Roger,
>>> I agree that requisite variety is a prerequisite for effective  
>>> control.
>>>
>>> Nick, why did you say "finite precision" in : " but it is applicable
>>> with
>>> abstract systems like money man hours and other finite precision
>>> systems." ?
>>> Please explain for a simple pilot...
>>>
>>> Thanks,
>>> Arthur
>>>
>>>
>>> -----Oorspronkelijk bericht-----
>>> Van: Forum dedicated to the work of Stafford Beer
>>> [mailto:[log in to unmask]] Namens John Waters
>>> Verzonden: woensdag 7 oktober 2009 16:10
>>> Aan: [log in to unmask]
>>> Onderwerp: Re: Control and the Law of requsite variety
>>>
>>> Forwarded:
>>>
>>> -------- Original Message --------
>>> Subject: Re: Control and the Law of requsite variety
>>> Date: Wed, 7 Oct 2009 14:48:06 +0100
>>> From: Roger Harnden <[log in to unmask]>
>>> To: [log in to unmask]
>>> References: <002801ca4719$e5c778d0$b1566a70$@nl>
>>> <[log in to unmask]> <[log in to unmask]>
>>>
>>>
>>>
>>> Perhaps, Arthur, it is more that requisite variety is a prerequisite
>>> for effective control, and that, should you not have this  
>>> prerequisite
>>> variety, then any 'control' you think you have will prove illusory.
>>>
>>> Roger
>>> On 7 Oct 2009, at 11:18, John Waters wrote:
>>>
>>>> Arthur Dijkstra wrote:
>>>>
>>>>>> Dear all,
>>>>>>
>>>>>> This forum keeps changing me and I like it.
>>>>>>
>>>>>> Often we refer to Ashby's law. When we refer to it when we  
>>>>>> speak of
>>>>>> control I think we miss something. Simply said requisite  
>>>>>> variety is
>>>>>> required but not sufficient for effective control. The  
>>>>>> controlling
>>>>>> system must have /relevant/ variety for the regulated system, not
>>>>>> just
>>>>>> variety in general.
>>>>
>>>> I wrote:
>>>>
>>>>> I believe the need for this distinction is recognized in the use  
>>>>> of
>>>>> the
>>>>> word "requisite" rather than (for example) "sufficient".
>>>>
>>>> Clarification from OED:
>>>>
>>>> requisite
>>>>   adj. & n.
>>>>   ~ adj. required by circumstances; necessary to success etc.
>>>>   ~ n. (often foll. by for) a thing needed (for some purpose).
>>>>   ~ requisitely adv. [ME f. L requisitus past part. (as REQUIRE)]
>>>>
>>>> John (:
>>>>
>>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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>>>>
>>>> For the Metaphorum Collaborative Working Environment (MCWE) go to:
>>> www.platformforchange.org
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>>>>
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>>>>
>>>
>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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>>>
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>>>
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> For more information go to: www.metaphorum.org
>>
>> For the Metaphorum Collaborative Working Environment (MCWE) go to:
>> www.platformforchange.org
>>
>> METAPHORUM eList Archive available at -
>> https://listserv.heanet.ie/ucd-staffordbeer.html
>>
>> Archive of CYBCOM eList available at -
>> http://hermes.circ.gwu.edu/archives/cybcom.html
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> For more information go to: www.metaphorum.org
>
> For the Metaphorum Collaborative Working Environment (MCWE) go to:  www.platformforchange.org
>
> METAPHORUM eList Archive available at - https://listserv.heanet.ie/ucd-staffordbeer.html
>
> Archive of CYBCOM eList available at - http://hermes.circ.gwu.edu/archives/cybcom.html
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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