I have to disagree with you Eric. I develop computer models for a living;
They are not EXACT, they are MODELS complete with simplifying assumptions
(Assume a cow is a sphere one-meter in diameter...). That is, they are
mathematical approximations that (hopefully) predict the real world.
Even if you ignore the assumptions, COMPUTER models are not exact since they
are implemented in digital computers. This means that precision is limited
by the number of bits used to store the various parameters.
Joe DiPietro
N2UF
----- Original Message -----
From: <MorgusMagnificen@aol.com>
To: <conrad@g0ruz.net>
Cc: <amps@contesting.com>
Sent: Tuesday, February 11, 2003 12:05 PM
Subject: Re: Spam Alert: Re: [Amps] The Philosophy of Science
> Okay, I sincerely apologize for the aggressive broadside. I am just sick
and
> tired of hearing all of the distortions of theoretical science and
> engineering that I hear EVERYWHERE . I hoped this group would have a
little
> more understanding of it. If your world ends at the 4th significant
figure,
> fine for you. For many others, the action doesn't even begin until the
6th -
> or 10th.
>
> One statement by you and others ( in some of those OTHER armchairs)
regards
> the term 'computer modelling'. There is somewhat of a semantic problem
here,
> as follows. The computer models which we use are EXACT, precise physical
> devices whose electronic equations we can write precisely. We can then
apply
> them in circuits and solve the circuit equations to any desired degree of
> accuracy. In the limit (this is a profound mathematical statement, which
> forms the basis of all numerical computation algorithms) these solutions
> converge to the exact answer (if the algorithm designer has not screwed
up!).
>
> The approximation comes in when we attempt to apply this exact model to a
> practical circuit. Again, the degree of agreement between the two is
limited
> by our ability to measure the real-world components, which we all know has
> practical as well as theoretical limits. So it is not the modelling
process
> which is 'inexact'. The error comes from our measurment limits, which we
> know, control, and can accurately predict.
>
> The laws of physics themselves are models. I posed the very relavent
question
> "is the formula R=E/I an exact model" and no one wants to take a stand on
> that, the most basic of all of our electrical 'laws'. That we can approach
> exactness only in the limit sense does not make it any less useful to us.
>
> I want to close this (although I am sure you would like to conrtinue to
hear
> me rant) by going back to where it began, and show how all of those who
have
> argued against me have badly distorted the issue. It started when Jeff
posted
> a very simple solution to a somewhat complex problem - the calculation of
> filter capacitance in a PS. I was, like others, initially suspicious of
his
> results but I wanted to check it out as accurately as possible before
> attacking his work. To do so, I made the most accurate calculation I could
of
> the same problem, so that if I were to raise a complaint, no one could
accuse
> me of basing it on an inexact calculation (i.e. an approximation, with
which
> the older power supply literature is filled .) So by comparison, my
> calculations were so precise (let's say they produced results accurate to
> .01%) that they were effectively exact in comparison to older data. To
most
> engineers I know, that constitutes an exact calculation. (What you may not
> realize is that this 'old' data which I always refer to was based on
highly
> approximated models - with our modern computers we do not have to severely
> approximate our models.)
>
> Does it really change anything if I change the wording to read 'highly
> precise' calculations instead of 'exact'? Would it convey any more or
less
> useful information to you? Would it make any difference when you finally
get
> back to your workshop to build your amp, for which you will be doing well
to
> get a filter cap that is within 10% of the predicted EXACT value?
>
> I would like to ask for a polling by everyone reading this (if you are
still
> awake) on the following: Does the fact that my calculations were
terminated
> at an accuracy of .01%, as opposed to the known errors of 10% or greater
in
> old data, mean that my calculations are not exact? And if not, how precise
> would I have to make them in order to qualify as a standard against which
to
> measure simple approximated calculations, such as Jeff's? Does it bother
you
> that I use the word 'exact' in the context of "high-accuracy, so high that
> its estimated error is too low to be of any concern" ?.
>
> Eric K8LV
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> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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