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From: Phil Richards (news_at_[hidden])
Date: 2005-10-21 05:04:10

On 2005-10-20, Kevin Lynch <krlynch_at_[hidden]> wrote:
> Deane Yang wrote:
> > A general dimension/units library is, I think safe to say, useful
> > anywhere one is doing mathematical computations in a practical setting.
> > Virtually any practical mathematical calculation uses well-defined
> > dimensions and units, and such a library would help guard against
> > incorrect formulas. But I don't have specific examples (my experience is
> > just as limited as yours); I'll have to let others, if any, speak up.
> Here's the set of examples I bring up every time this discussion rears
> its head ...
> 1) Particle and nuclear physics use a "natural units" system in
> theoretical calculations where length and time have the same units, and
> energy, mass, and momentum have the same units, and the two units are
> just the inverse of each other. You would't WANT to use SI in this
> field, because the orders of magnitude aren't even close to useful.
> Additionally, your fundamental unit is energy, which is a derived unit
> in SI.

Can you give an example of an equation and explain what dimensional
analysis is able to be performed? Off hand, it looks like there
is only one dimension to keep track of - is that right?

But, my original supposition stands: you wouldn't want dimensional
analysis that was using SI stuff to interact with dimensional analysis
at used in particle physics because they don't match. You would, in
fact, want the library to prevent such operations, I would guess.

> SI is _A_ useful system of dimensions and units, but it is geared to
> physical measurements used in commerce, trade, and engineering. It is
> not in any way a statement about mathematics, and is often the wrong
> choice for a unit system in fields of basic science.

I certainly don't disagree with that statement. But I only really have
experience of dimensions and units that are compatible with the SI
view of things, so it is practically impossible to design a library to
support other modes without knowing more about how they operate...
(That, I suspect, is true for all the people who've tried over the last
couple of years.)


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