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UCD-STAFFORDBEER  October 2009

UCD-STAFFORDBEER October 2009

Subject:

Re: Control and the Law of requsite variety

From:

Nick Green <[log in to unmask]>

Reply-To:

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

Date:

Wed, 7 Oct 2009 18:05:02 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (152 lines)

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: 
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>
> METAPHORUM eList Archive available at - 
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