Re: [boost] Re: Units libraries... (long reply)

From: Phil Richards (news_at_[hidden])
Date: 2004-01-13 13:06:45

On Sun, 11 Jan 2004 16:52:22 -0500, Dan W. wrote:
[... stuff zapped ...]
> Note that if the absolute point happens to be absolute in more than just a
> relative sense, it may actually enable addition:  Adding degrees Celsius
> or Farenheit makes no sense; but adding Kelvins does, at least in some
> contexts.

I don't see the difference between Celsius, Fahrenheit, and Kelvin if you
are looking at them in pure absolute (or relative) terms.  It makes no
more sense to add 1K-above-zero-K to 1K-above-zero-K than 1C-above-zero-C
to 1C-above-zero-C.  It makes as much sense to add 1K (relative world) to
1K (either absolute or relative) as it does to add 1C (relative world) to
1C (either absolute or relative).  Both systems have a defined zero-point.

I think you're accidentally introducing a special case that isn't really
one.  (And nobody trying to "design" a library likes special cases :-)

Actually, I find it difficult to think of "absolute" quantities as
anything but standalone quantities that live somewhat to the side of this
discussion.  Yes, they are clearly related, but you can't use an "absolute
unit" as a dimension in dimensional analysis (by any "normal" definition
of dimensional analysis, and I'm not even talking about "physical
quantities" here). All the things you want dimensional analysis to do for
you are broken by using "absolute dimensions" since the key thing about
dimensional analysis is that it calculates the unit of things when they
are multiplicatively combined - absolute quantities *can't* be multiplied
by anything.

phil
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