[boost] Re: Physical quantities

From: Andy Little (andy_at_[hidden])
Date: 2004-01-15 01:48:23

"Deane Yang" <deane_yang_at_[hidden]> wrote

> Way at the beginning,
> I expressed some confusion about what a "dimension" was. I have yet
> to see anyone articulate clearly and precisely what the definition
> of a "dimension" is (please chime in if you have one!). Is it something
> like this:

You say you understand the mathematical concepts behind dimensional
analysis. I am not qualified to tell if you do or you dont. However if you
do, it would be extremely useful if you wrote a paper on the subject. Bear
in mind that it should be written with someone like me in mind. I have two
kinds of technical books. Some I use frequently, some I don't. The ones I
use are those where the author has taken the time to consider things from a
laymans perspective. Examples C++ 3rd Ed., Horovitz and Hill, The Art of
Electronics. The guys that wrote these are clever enough that they dont need
to show how clever they are. In other technical books I get the impression
that the authors really need to prove how clever they are. So, I hope when
(if) you write your paper you bear this simple point in mind. Put simply, if
I cant understand it then it is completely useless to me.

If  I had to write a paper on the subject, I would use the SI unit system as
the basis of examples. It is universal. You and others may have issues with
it, but it would therefore provide a balanced approach. Look at its
strengths. Then point out its weaknesses. After examining D.A in context of
SI, perhaps you could give an example of how a user might go about designing
their own quantity system. If that was achieved that would be invaluable to
me, and anyone else who is trying to get to grips with 'quantities'.

A good way to start a paper might be with definitions for: dimension,
quantity, unit and value. (Some D.A...some not). May I suggest external
research.
One way to define these things is by means of examples: A is an x, B is not
an x etc.
Unfortunately once outside the world of maths... life gets complicated..
have some sympathy with the SI guys.

Criticism is easy... creation is extremely difficult.
Maths takes place in the mind...physics takes place in the world.

I emphasise again a definitive paper would be extremely useful to me in
getting to grips with this subject.

regards
Andy Little