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From: Matthias Schabel (boost_at_[hidden])
Date: 2004-01-09 13:47:03

> Phil Richards wrote:
>> require that either "fahrenheit(32) + fahrenheit(32) ==
>> fahrenheit(32)" or
>> "celsius(0) + celsius(0) == celsius(0)"
> Hmmm... does adding temperatures make sense in the first place...?...

This absolute vs. relative quantity issues arises pretty much
everywhere. For example,
if I have two points along the x-axis, one at 7 meters and another at
12 meters, what does
it mean to add the two? Nothing really. We can add an increment in
distance to either one,
to get a new absolute position or we could add two increments to get
another increment, but
adding two absolute quantities doesn't really make sense. In the same
way, if I write

32*_fahrenheit+32*_fahrenheit = 64*_fahrenheit

it makes perfect sense if one or both of the terms on the left is a
relative quantity, but not
if both are absolutes...

Matthias Schabel, Ph.D.
Utah Center for Advanced Imaging Research
729 Arapeen Drive
Salt Lake City, UT 84108
801-587-9413 (work)
801-585-3592 (fax)
801-706-5760 (cell)
801-484-0811 (home)
mschabel at ucair med utah edu

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