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From: Kevin Lynch (krlynch_at_[hidden])
Date: 2005-10-20 14:21:06

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.

2) Cosmology and astrophysics are in a similar situation, but use a
different set of natural units.

3) SI doesn't include things like currency, and doesn't admit the
possibility that unit conversions change with time.

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.

Kevin Lynch				voice:	(617) 353-6025
Physics Department			Fax: (617) 353-9393
Boston University			office:	 PRB-361
590 Commonwealth Ave.			e-mail:	 krlynch_at_[hidden]
Boston, MA 02215 USA

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